MEMCAL SCHOOL ■ f fit w tlG. 1. Convex Surface of Cerebrum Cortical Areas. Fig. II. Cortical Areas on Medial Surface of Cerebrum. Digitized by the Internet Archive in 2007 with funding from IVIicrosoft Corporation http://www.archive.org/details/anatomybr.ainspinOOsantrich ANATOMY OF THE Brain AND Spinal Cord WITH SPECIAL REFERENCE TO THE GROUPING AND CHAINING OF NEURONES INTO CONDUCTION PATHS. For Students and Practitioners. HARRIS E.^SANTEE, M. D., Ph. D., Professor of Anatomy in the College of Physicians and Surgeons, Medical Department, University of Illinois; Professor of Anatomy in Harvey Medical College, Chicago. WITH A PREFACE BY WILLIAM T. ECKLEY, M. D., Professor of Anatomy in the Medical and Dental Departments, University of Illinois. THIRD EDITION REVISED AND ENLARGED. Chicago : E. H. COLEGROVE. 1903. Copyright, 1903, by Harris E. Santee Chicago, III. Q HA4 5 %-J A PEEFACE. It is with pleasure I respond to the author's invitation to write an introductory page, and I sincerely acknowledge the compliment. My remarks, necessarily few, are in the nature of convic- tions founded on a study of this and the previous edition, on a comparison of this work with others of similar nature, on a long personal acquaintance with the author, an appreciation of his conception of anatomy and his methods of teaching the same. To peruse the book, is to convince one of its value as a contribution to our literature; to know the author, is to enhance the desirability of the book. It is needless to comment on detail, logical arrangement and orderly subordination of minor to major parts, looking to the ultimate desideratum of a mionograph on the brain and spinal cord, for the use of students and practitioners. Such features are possessed by books in general. My remarks will be directed to what I consider superior qualities, these inci- dentals which relieve the tedium of scientific detail and in- delibly impress the practical value of a subject. The composition, relation and contour of the operculum and posterior part of the inferior frontal gyrus, become more interesting, when it is shown that "They constitute the re-' gion of speech.'' In like manner, that "The temporal lobe is the probable seat of the centers of taste, smell and hear- ing," and that "The ascending frontal, ascending parietal and superior parietal convolutions are the best known motor areas of the cortex," are physiological observations which III 5240.') PREFACE. instruct and fascinate alike. In this manner, throughout the book, the author invokes function of a region to gain an anatomical end. The olfactory lobe in man, represented by the bulb, tract, trigone, area of Broca and anterior perforated space, finds the lobar antecedent and a reason for its name, in the lower animals, and in this way the author elucidates a point which were incomprehensible to the student without such compari- son. The adult human brain is complex, stable, coherent and heterogeneous, but as a simple, comprehensible means to a great teaching expedient, the author invokes the precepts of embryology to show that this composite brain had a simple vesicular prototype whose simple cavity became complex ven- tricles, whose simple spongioblasts became complex neu- rogliar network, whose simple primitive neuroblasts became neurones, with cell-bodies and dendrites in cortex and ganglia, and medullated axones forming the white substance of the brain. Numerous illustrations might be drawn from every chap- ter of the book to show like superior teaching qualities, but observations which even the most casual perusal of the book itself makes apparent add nothing of value to criticism. In his presentation of the tracing of impulses, Dr. Santee has done more to simplify the complex conduction paths to and from the brain than any author after whom I have read. 'In this respect his book excels, and must appeal to teachers of anatomy, practitioners of medicine and students alike. The conception of a motor nerve according to many is a tangible band of white matter (as the anterior tibial) asso- ciated above with a plexus. Dr. Santee's conception, how- ever, is a path composed of numerous neurones extending IV PREFACE. from a cortical area in the neighborhood of the Rolandic fissure through the pyramidal tracts of the spinal cord to both co-ordinated and inco-ordinated muscles. His conception of a sensory conduction path is not the ordinary one which leaves the student in doubt as to the location of trophic cells of centripetal nerves^ but the embryological one which recog- nizes sensory spinal and sensory cranial nerves as growing toward and into the brain, from posterior root and cephalic ganglia respectively. Such a conception of motor and sen- sory nerves enables a student to read intelligently the de- generations. Again, it is superior teaching that ascribes function to the definite tracts of fibers, to- wit : "The pyram- idal tracts are motor;" "Gower's tract probably carries thermic and pathetic impulses;" "GolFs column carries im- pulses of the muscular sense;" "All varieties of impulse are carried by Burdach's column;" "The direct cerebellar tract conveys impulses of equilibrium received especially from the viscera." In conclusion, Dr. Santee's "Anatomy of the Brain and Spinal Cord" is concise, exact, scholarly, and possesses su- perior qualities in the manner of elucidation; it gives the most comprehensive exposition of the conduction paths of the brain and spinal cord of any book in our language, and is destined to become popular everywhere. Very truly, W. T. ECKLEY. CONTENTS. Chapter I. PAGE. Membranes of the Brain 1-6 Dura Mater 1-4 Middle meningeal artery 3 Arachnoid 4-5 Pia mater 5-6 Table 1. Grand divisions of brain 6-7 Chapter II. The Cerebrum. 8-51 Section i. Exterior surface 9-24 Convex surface 9-14 Fissures 9-11 Lobes and convolutions 11-14 Medial and tentorial surface 14-17 Fissures 14-16 Lobes and convolutions 16-17 Basal surface 17-24 Medial structures 18-21 Lamina cinerea , 18 Tuber cinereum 18 Pituitary body 19 Corpora albicantia 19 Optic commissure 20 Lateral structures 21-24 Orbital lobe 21 Island of Reil 22 Olfactory lobe 22 Section 2.. Interior surface of cerebrum 24-51 Internal capsule , 25-28 VII CONTENTS. PAGE. Corpus callosum 28-30 General cavity of cerebrum 30-31 Fornix 32-33 Septum lucidum 33 Fifth ventricle 33-34 Lateral ventricle, body 34-42 Corpus . striatum 35-37 Taenia semicircularis 37 Optic thalamus 37 Choroid plexus 38 Cornua, anterior, posterior and middle 38-42 Third ventricle 42-43 Boundaries 43-44 Roof epithelium 44-45 Pineal body 45-46 Velum interpositum 46-47 Choroid plexus and tela 46 Anterior commissure 47 • ; Optic thalamus 48-50 Hypothalamic region 50 Geniculate bodies, external and internal 50-51 Chapter III. The Mid Brain 52-65 Surfaces 52-54 Interior 54-65 Crustae 54-56 J Intermediate bundle 55 Temporal cerebro-corticopontal tract 55 Pyramidal tract 55-56 Frontal cerebro-corticopontal tract 56 Substantia nigra 56-57 Tegmentum 57-65 Aqueduct of Sylvius 58 Corpora quadrigemina 59 Internal geniculate body 60 Fibers of tegmentum 60-65 Posterior longitudinal bundle 61 CONTENTS. PAGE. Anterior longitudinal bundle 62 Fillet or lemniscus 6^-63 Superior peduncle of cerebellum 64 Olivary bundle 64 Tract from red nucleus 65 Chapter IV. Gray and White Matter of Cerebrum and Mid Brain.. 66-99 Neurone 66-70 Sustentacular tissue 67 Cortical gray matter 70-76 Motor areas 70-71 Somaesthetic area (common sensory) 70 Special sense areas 71 Association centers 71-72 Effect of lesions in special areas 72 Layers of typical cerebral cortex 72-74 Exceptions 74-76 Ganglionar gray matter 76-84 Corpus striatum 76-78 Caudate nucleus 76 Lenticular nucleus 76 Lesions in corpus striatum 77 Optic thalamus 78-81 Nuclei of thalamus 78-79 White matter of thalamus 79-80 Lesions of lateral nucleus and nucleus of pulvinar 78 Nucleus hypothalamicus (Luysi) 81 Nucleus ruber (red nucleus) 81 Geniculate bodies 82 Corpora quadrigemina 82-83 Substantia nigra 83-84 Central, or ventricular, gray matter 84-85 Lamina cinerea and tuber cinereum 84 Middle commissure (massa intermedia) 84 Nuclei of oculomotor and trochtear nerves 84 Projection fibers — Motor. 85-89 Internal capsule and crusta 85-89 IX CONTENTS. PAGE, Pyramidal tract 86-89 Cranial fibers 87 Upper extremity fibers 87 Trunk fibers 88 Lower extremity fibers 88 Frontal cerebro-corticopontal tract 86 Temporal cerebro-corticopontal tract 86 Intermediate bundle 86 Tegmentum 88 Descending tract from red nucleus 88 Anterior longitudinal bundle 88 Lesions of motor tracts 89 Projection fibers — Sensory 89-91 Tegmentum 89 Internal capsule — common sensations 89-91 Three systems of Flechsig, or cortical fillet 89-90 Ansa peduncularis 89 Ansa lenticularis 89-90 Anterior stalk of thalamus 90 Lesions of cortical fillet 90 Internal capsule — special sensations 90-91 Acustic radiations 90 Optic radiations 90-91 Lesions of acustic and optic radiations 90-91 Commissural fibers 91 Corpus callosum 91 Anterior commissure 91 Lyre, or commissura hippocampi 91 Association fibers 91-94 Short 91 Certain lesions of 92 Long 92-94 Cingulum 92 Fornix.. 92 Uncinate fasciculus 93 Lesion of , 93 Superior longitudinal fasciculus 93 Interruption of 93 X CONTENTS. PAGE. Inferior longitudinal fasciculus 93 Fasciculus occipito-frontalis 93 Perpendicular fasciculus 94 Blood supply of cerebrum and mid-brain 94-99 Cortical system of arteries 95-96 Ganglionar system of arteries 96-97 Veins 98 Lymph spaces 99 Chapter V. Hind Brain 100-128 Section i. Cerebellum 100-118 Functions 100 Hemispheres and vermis 100-101 Medullary vela 101-102 Cerebellar peduncles 101-103 Superior surface 103-107 Fissures and lobes 103-107 Inferior surface 107-111 Fissures and lobes 107-111 Interior 111-118 Gray matter 111-114 Cortical 111-113 Functions and lesions of 113 Ganglionar 113-114 White matter 114-118 Projection fibers 114-116 Cerebellar peduncles 114-116 Commissural fibers 116 Association fibers 117 Blood supply 117-118 Section 2. Pons 118-128 Surfaces '. 119-120 White matter of Pons 120-125 XI CONTENTS. PAGE Transverse fibers 121-122 Ventral 121 Middle 121 Dorsal 121-122 Longitudinal fibers 122-125 Ventral (pyramidal) 122 Middle (formatio reticularis) 123 Fillets 123-124 Posterior longitudinal bundle 124 Anterior longitudinal bundle 124 Olivary bundle 124-125 Tract from red nucleus 125 Root of trifacial nerve 125 Dorsal longitudinal fibers 125 Superior cerebellar peduncles 125 Valve of Vieussens 125 Gray matter of pons 126 Nuclei pontis 126 Nuclei of formatio reticularis 126 Cranial nerve nuclei 126 Superior olivary nucleus 126 Lesions of pons 127 Blood supply of pons 127 Chapter VL Medulla Oblongata 128-149 Surfaces 129-133 Ventral 130-131 Lateral 131-132 Dorsal 132-133 Interior — white matter 133-145 Formatio reticularis and raphe ; 134-135 Transverse fibers 135-136 External arciform anterior and posterior 135 Internal arciform 136 Sensory, or fillet, decussation 136 Cerebello-olivary tract 136 Dorso-ventral fibers — nerve roots 136-137 XII CONTENTS. PAGE. Longitudinal fibers 137-145 Pyramids 138 Formatio reticularis alba 138-139 Interolivary fillet 139 Posterior and anterior longitudinal bundles. .139-140 Formatio reticularis grisea 140-141 Antero-lateral ground bundle 141 Triangular tract (Helwig) 141 Antero-lateral cerebellar tracts 141-142 Tract from red nucleus 142 Fasciculus gracilis 142-143 Fasciculus cuneatus 142-143 Fasciculus Rolandi 143-144 Direct cerebellar tract 144 Restiform body 144-145 Fasciculus solitarius 145 Fasciculus teres 145 Interior — gray matter 146-149 From anterior horn 146-147 From posterior horn 147 Added nuclei 147 149 Lesions of medulla 149 Chapter VI L Fourth Ventricle 150-158 Boundaries 150-153 Eminentia teres 151-152 Fovea superior 151-152 Locus coeruleus 151-152 Trigonum hypoglossi 152 Trigonum vagi 152-153 Trigonum acustici .... 152-153 Table 1 1 . Origins of cranial nerves 153-158 Ventral nuclei, motor 156-157 Dorsal nuclei, sensory .^ 157-158 Blood supply of medulla oblongata 158 Chapter VIII. Meninges of Spinal Cord 159-161 Dura mater 159 XIII CONTENTS. PAGE. Arachnoid 160 Pia mater 160-161 Ligamentum denticulatum 161 Nerve and blood supply 161 Chapter IX. The Spinal Cord ...162-184 Enlargements of cord 163 Ventricle of cord = 163 Surface 163-165 Fissures 163-165 Gray matter of cord 165-171 Substantia gelatinosa 166 Substantia spongiosa 166 Anterior horn of crescent 166-168 Lesions of 167-168 Center of crescent 168-169 Posterior horn of crescent 169-170 Gray commissure of cord 170-171 White matter of cord 171-182 Anterior commissure 171-172 Nerve roots 179-182 Tracts (longitudinal) 172-179 Ascending 172 Descending 172 Mixed (ascending and descending) 173 Antero-lateral ground bundle 173-174 Anterior and posterior longitudinal bundles. .173-174 Uncrossed (direct ) pyramidal 174 Antero-lateral descending cerebellar 174 Antero-lateral ascendmg cerebellar 175 Triangular (Helwig) olivary of cord 175 Direct cerebellar. . 175-176 Crossed pyramidal 176-177 Crossed descending from red nucleus 176 Lesions of pyramidal tracts 177 Marginal (Lissauer) 177 Postero-lateral (Burdach) 177-178 XIV CONTENTS. PAGE. Cornu commissural 178 Septo-marginal 178 Comma 178 Posteromedian (Goll) 179 Lesions in posterior columns 179 Roots of spinal nerves 179-182 Anterior roots 180 Origins— superficial and deep 180 Lesions of lower motor neurones 180 Posterior roots 180-182 Central terminations 181 Superficial (apparent) 181 Deep (real) 181-182 Lesions of posterior roots 182 Blood supply of the cord 182-184 Chapter X. Tracing of Impulses 185-201 Efferent, or motor, paths, through 185-190 Pyramidal tracts 185-186 Frontal cerebro-corticopontal tract 186-187 Temporal cerebro-corticopontal tract 187 Intermediate bundle 187 Red nucleus — direct and indirect 188 Short fiber paths (formatio reticularis) 188-190 Facial paralysis, nuclear and nerve trunk 189 Abducent paralysis and irritation 189-190 Afferent paths, general sensation 190-193 Columns of Goll and Burdach 190-192 Direct 190-191 Indirect 191-192 Cranial nerves and medial fillet 191 Direct cerebellar tract 191-192 Antero-lateral ascending cerebellar tract 192-193 Short fiber paths (antero-lateral ground bundle).... 193 Lesions of sensory tracts. . 193 Afferent paths, special sense. 194-197 Olfactory 194 XV CONTENTS. PAGE. Optic 194-195 Auditory .' 195-197 Cochlear 195 Vestibular 196 Gustatory 197 Lesions of special sense tracts 197 Reflex paths 198-201 Varieties of reflex arcs 198 Spinal reflexes 198-199 Defecation, etc 198-199 Cranial reflexes 199 Spinal and cranial reflexes 199-200 Cranial and spinal reflexes 200-201 Respiratory '. 200 Auditory 200 Pupillary 200-201 Chapter XI. Embryology of Brain and Spinal Cord 202-224 Neural crest 202-204 Cranial nerve ganglia 202-203 Spinal and sympathetic ganglia 203-204 Neural tube , 204-224 Three histologic layers 205 Neurogliar 205 Mantle 20J Ependymal 205 Flexures 206 Table III. Brain vesicles and derivatives 207-208 1. Prosencephalon 208-213 Hemisphere vesicles 208-213 Foramen of Monro and lateral ventricles. 208 Olfactory lobe 208 Fissures, primary and permanent 209-210 Special thickenings 210-211 Fusion of Hemispheres with one another. . 211-212 Fusion with thalamencephalon 212 Velum interpositum 212-213 XVI CONTENTS. PAGE. 2. Thalamencephalon 213-214 Optic vesicle 213 Thalamus 214 External geniculate body 214 Posterior commissure 214 Pineal body. 214 3. Mesencephalon 214-215 Tegmentum 215 Corpora quadrigemina 215 Internal geniculate body 215 Aqueduct of Sylvius 214 Substantia nigra 215 Crustae 215 4. Epencephalon 215-216 Cerebellum 215-216 Vermis 216 Hemispheres , 216 Penduncles 216 Pons 216 Nuclei of pons 216 Nuclei of cranial nerves 216 5. Metencephalon 217-219 Internal surface 218 External surface 218 Three histologic layers 218-219 Ependymal 218 Mantle 218-219 Neurogliar 219 Spinal cord 220-224 Ventral and dorsal zones 220-221 Histologic layers , 221 Mantle layer — gray substance 221-222 Tracts of fibers— when meduUated 222-223 Fissures of cord 223-224 XVII CHAPTER I. THE MENINGES OF THE BRAIN.i Three membranes invest the brain and spinal cord. They are, from without inward, the Dura Mater, the Arachnoid, and the Pia Mater. Each membrane forms a protecting sheath for the cranial or spinal nerves piercing it. THE DURA MATER.2 Structure and Relations. — It is a very dense and inelastic membrane composed of white fibrous and yellow elastic tissue. It is lined with flat endothelial cells which constitute its internal surface. The dura is made up of two layers, but they are in most places closely united. The external layer constitutes the endosteum of the cranial bones. It is their nutrient membrane. Through the cranial foramina and sutures it is continuous with the external periosteum. The internal layer of the dura separates from the outer layer, at the foramina, to form sheaths for the nerves and, along the sinuses, to form the internal boundary of those venous spaces and to produce the great incomplete partitions, called processes, which project centrally into the great fissures of the brain. Processes. — From the inner surface of the dura the great processes^ are given off. The falx cerebri and falx cerehelU hang vertically in the great longitudinal fissure of the cere- (1) Meninges encephali. (3) Processus durae matrls. <2) Dura mater encephali. 2 THE BRAIN AND SPINAL CORD. brum and the posterior notch of the cerebellum ; and, into the great transverse fissure, extends horizontally the ten- torium cerebelU. The falx cerebri is attached in front to the crista galli and behind to the internal occipital protuber- ance and superior surface of the tentorium; the falx cere- belli continues from the inferior surface of the tentorium, along the occipital crest, to the posterior border of the fora- men magnum. The attachment of the tentorium cerebelli is to the internal protuberance and the lateral arms of the crucial ridge forward to the petrous bone; and, then, it is along the superior border of the petrous bone to the clinoid processes of the sphenoid. A large median notch between its anterior border and the dorsum ephipii, incisura tentorii, transmits the mid-brain. The diaphragm sellce is a small centrally perforated sheet of dura which covers the pituitary fossa. Sinuses. — Large venous passages lined with endothelial cells, and called sinuses, are situated between the layers of the dura. In the convex and in the free border of the falx cerebri are, respectively, the superior^ and the inferior^ lon- gitudinal sinus. The superior extends from the foramen cascum back to the torcular HeropMli,^ at the internal occip- ital protuberance. Joining the common vein^ of Galen, at the margin of the tentorium, the inferior longitudinal sinus becomes the straight,'^ whose course is through the middle of the tentorium to the torcular. The occipital sinus^ (or sinuses) traverses the falx cerebelli from the foramen mag- num upward to the same point. In the torcular Herophili the lateral sinv^es^ rise. Grooving the horizontal arms of (4) Sinus sag-ittalis superior, et inferior. (5) Confluens sinuum, (6) Vena cerebri magna. (7) Sinus rectus. (8) Sinus occipitalis. (9) Sinus traversus (singr.). THE MENINGES OF THE BRAIN. 3 the crucial ridge, each runs outward in the tentorium to the base of the petrous bone, where it receives the superior petrosal sinus; it then turns downward through the sig- moid fossa and unites with the inferior petrosal sinus in the jugular foramen. Situated on either side of the sella Tur- cica is a continuation of the ophthalmic vein, the large cavernous sinus,^^ whose division at the apex of the petrous bone forms the two petrosal sinuses.^^ The circular sinus^^ (around the sella) joins the two cavernous to each other; and the inferior petrosal sinuses communicate with one an- other through the transverse or basilar sinus.'^^ The petrosal sinuses, from the bifurcation of the cavernous sinus, follow outward the corresponding border of the petrous bone; the superior petrosal empties into the lateral sinus at the base of the petrous bone; and the inferior petrosal, running outward to the jugular foramen, unites with the lateral sinus in forming the internal jugular vein. Along and within the superior longitudinal sinus are the Pacchionian bodies.^* They are enlarged villi of the arach- noid, and seem to afford an outlet for the sub-arachnoid fluid into the superior longitudinal sinus. The arteries which supply the dura are the anterior and posterior ethmoidal from ophthalmic; from internal carotid, the anterior meningeal ; the great and small meningeal which are branches of internal maxillary; meningeal branches of the ascending pharyngeal and occipital; and the posterior meningeal from the vertebral artery. The middle meningeal^^ is largest. It is accompanied by (10) S. cavernosus. (11) Sinus petrosus superior, et inferior, (12) S. circularis. (13) S. basilarls. (14) Granulatlones arachnoldeales. (16) Arteria menlngea media. 4 THE BRAIN AND SPINAL CORD. a vein and surgically is important because of its course over the motor area. Ascending from the foramen spinosum it divides near the upper border of the squamosa into two large branches, the anterior and posterior. The posterior runs horizontally backward just below the squamo-parietal suture and then ascends over the posterior half of the parietal bone. The anterior branch runs upward a half-inch behind the coronal suture. It may be located, according to Quain, at one inch, one inch and a half, and two inches behind external angular process and above the zygoma. The following nerves give branches to the dura: — troch- lear, ophthalmic, Gasserian ganglion, the tenth and twelfth cranial; and the sympathetic. The motor fibers supply the meningeal arteries. Six points of difference in the dura of the cord. — Absence of processes, of sinuses, of Pacchionian bodies, and of perios- teal function. It is covered on both surfaces by endothelium and separated from the vertebrae by areolar tissue, fat and the meningo-rachidian veins. ARACHNOID OF BRAIN. In structure it is a delicate, fibrous, web-like membrane covered externally with endothelium. Internally it is joined to the pia mater by innumerable fibrous trabeculae, the sub- arachnoid tissue. The trabeculae and all spaces formed by them possess a single layer of endothelial cells. Conical elevations of fibrous tissue with their investing epithelium constitute the villi seen on the outer surface. Relations. — The arachnoid^^ follows the inner surface of the dura and is prolonged, as a sheath, upon the nerves which pierce it. It does not dip into the sulci of the brain. From (16) Arachnoidea enciephall. THE MENINGES OF THE BRAIN. 5 the pia it is separated by the subarachnoid spaces.^ "^ The cm- tenor subarachnoid space (cisterna pontis, interpeduncularis et chiasmatis), in front of the medulla, pons and mid-brain and between the temporal lobes of the cerebrum; and the posterior (cisterna cerebello-medullaris) , between the me- dulla and cerebellum, contain most of the subarachnoid, fluid. The posterior communicates with the fourth ventricle through the foramen of Magendie^^ and the foramina of Key and Retzius.^^ The vessels seen for a short distance in the arachnoid belong to the pia mater. Its nerves are doubtful. Perhaps branches of the inferior maxillary, of the facial and of the spinal accessory supply it. In the arachnoid of the cord fewer trabeculae join it to the pia; and these, in great part, are collected to form a fenes- trated septum in the posterior median line. The medulli- epinal veins are covered by the arachnoid, lying between it and the pia. PIA MATEE OP TEffi BRAIN.20 Structure. — It is a vascular membrane composed of a close network of veins and arteries held together by fibro-elastic areolar tissue. The endothelium covering its outer surface is contiuuous with that of the subarachnoid trabeculaB and spaces. Relations. — The pia closely follows the brain sur- face. Internally, it sends supporting trabeculss into the brain, which transmit blood-vessels; and externally it forms an investing sheath for the cranial nerves. TVo important processes are formed by it; the velum interpositum (which forms the superior choroid tela^i) is tucked into the choroid (17) Cavum subarachnoldeale (sing.). (18) Apertura medlana ventricull quartl. (19) Apertura lateralis ventriculi quart! (slng.)> (20) Pia mater encephali. (21) Tela choroidea ventriculi tertii. O THE BRAIN AND SPINAL CORD. (anterior great transverse) fissure between the fornix and the inter-brain. A second process is tucked in over the fourth ventricle, between the medulla and cerebellum. It forms the inferior choroid tela,22 which roofs over the inferior part of the fourth ventricle, and is of triangular shape. The inferior choroid tela is pierced by three foramina (Magen- die, and Key and Retzius). They open into the fourth ventricle. The arteries of the pia are the anterior, middle and pos- terior cerebral, the anterior and posterior choroids, and the anterior and posterior inferior cerebellar and superior cere- bellar with many branches. Veins are numerous in the pia; the veins of Galen and of the choroid plexuses of the lateral, third and fourth ventricles and the basilar vein; cerebral veins;, superior, medial and inferior; and superior, lateral and inferior cere- bellar veins. All of them empty into the sinuses. Seven cranial nerves — 3rd, 5th, 6th, and 7th, 9th, 10th and 11th — and the sympathetic supply the pia mater and its blood-vessels. The pia mater of the spinal cord has two layers, the outer of which is the more vascular and contains the spinal arteries and the tributaries of the meduUi-spinal veins. It forms three processes, namely, the anterior septum, which occupies the anterior median fissure, and the ligamentum denticu- latum of each side. TABLE 1. GRAND DIVISIONS OF BRAIN. The brain may be conveniently studied in four grand divisions : (22) Tela choroidea ventriculi quarti- THE MENINGES OF THE BRAIN 7 I. Cerebrum,23 composed of — 1. Heinisplieres,2* which include: Their cortex and medulla. Corpora striata, and Olfactory lobes. With connecting links of the hemispheres : Corpus callosum. Fornix, Commissura hippocampi and Anterior commissure; and 2. Inter-brain,25 or Thalamencephalon, which in- cludes : Lamina cinerea, Tuber cinereum and infundibulum, Corpora albicantia. Optic thalami. Middle commissure, and posterior (in part). Pineal body, External geniculate bodies. Optic tracts and commissure. II. Mid-brain, Cms Cerebri, or Pedunculus Cerebri^^ Crustae, (the bases or pedes pedunculi) Substantia nigra Tegmentum Corpora quadrigemina Internal geniculate bodies. III. Hind-brain27-_ Pons Cerebellum. IV. After-brain^s — Medulla. (23) Prosencephalon. (26) Mesencephalon. (24) Telencephalon. (27) Metencephalon. (25) Diencephalon. (28) Myelencephalon. CHAPTER II. THE CEREBRUM. The cerebrum is that part of the brain which especially characterizes man. In man only does it reach such predom- inant development. Though a mere outgrowth of the an- terior brain-vesicle in the beginning, it completely overshad- ows all other parts of the brain by the seventh month of em- bryonic life, extending farther forward, backward and lat- eral ward than any other part. Reference to the table given above shows that the cerebrum is made up of the hemispheres and the inter-hrain. It constitutes an ovoid mass, flattened inferiorly, which fills the vault of the cranium and rests, be- low, upon the floor of the cranial cavity in the anterior and middle fossae and upon the tentorium cerebelli over the pos- terior fossa. Viewed from above, it is sufficiently round to suggest a sphere ; and, being divided in the median line by the great longitudinal fissure, the lateral halves are called hemispheres. In the floor of the great longitudinal fissure the corpus callosum can be seen joining the hemispheres to- gether; and beneath it, concealed from view, are the fornix, anterior commissure, and commisura hippocampi. Those are the connecting links, proper, of the hemispheres. Inferior to them, is found the inter-brain. The latter forms an addi- tional union of the hemispheres, as may be seen by viewing the base of the brain. In order to fix important landmarks and to learn the location and relations of the gross structures THE CEREBRUM. 9 of the cerebrum, it is necessary to study in detail the topogra- phy of the exterior and interior surface. It is that with which the present chapter deals. For the minute anatomy of the cerebral structures, see Chapter IV. Section 1. The Exterior Surface. The exterior surface of the cerebrum^ is composed of a thin sheet of gray matter varying in thickness from one- sixth to one-quarter of an inch. That gray matter forms a bark-like covering for the underlying white substance and is, therefore, called the Cortex. It is thrown into irregular elongated folds named Convolutions, or Gyri, by deep linear depressions, which greatly increase the relative amount of cortical substance. The linear depressions are called Fis- sures, or Sulci; and, in consequence of them, the gray sub- stance is increased in bulk to 58^ per cent of the entire cere- brum (De Eegibus). The exterior surface is conveniently studied in three re- gions, namely, the Convex Surface, the Medial and Tento- rial Surface, and the Basal Surface. FISSURES OF the CONVEX SURFACE.^ Two fissures are very extensive. The great longitudinal fissure^ separates the hemispheres of the cerebrum. It con- tains the falx cerebri. The cerebrum is separated from the cerebellum by the great transverse fissure.* This fissure continues forward above the mid-brain, and terminates in the cerebrum between the inter-brain and the hemispheres as choroid fissure. The tentorium occupies its posterior part. The fissura choroidea contains the velum interpositum. Three (1) Prosencephalon. (2) Facies convexa. (3) Fissura longitudinalis cerebri. (4) Fissura transversa cerebri. 10 THE BRAIN AND SPINAL CORD. interlobular fissures^ are found on the convex surface of each hemisphere : (1) The Fissure of Sylvius^ begins in the vallecula at the base of the brain. It runs outward between the frontal and the temporal lobe^ along the lesser wing of the sphenoid bone ; and^ turning upward, on the convex surface it divides into an anterior, a vertical and a horizontal ramus. Into the frontal lobe project the small anterior and vertical rami. They are separated by the foot (posterior end) of the inferior frontal gyrus, called the frontal operculum (operculum, a cover). Below the anterior ramus is a knuckle of the same frontal convolution which forms the orbital operculum; and, between the vertical and horizontal rami, is located the fronto-parietal operculum, constituting the connecting gyrus between the precentral and postcentral convolutions. The opercula cover the island of Eeil. The horizontal limb of the Sylvian fissure separates the temporal lobe from the parietal. Near the crotch and within the fissure of Sylvius is situated the island of Eeil. A line drawn from the Sylvian point, one and one-quarter inches behind the external angu- lar process of the frontal and one and a half inches above the zygoma, backward to a point three-quarters of an inch below the parietal eminence, lies directly over the horizontal ramus of this fissure. (2) Fissure of Rolando. — Beginning just above the hori- zontal limb of the fissure of Sylvius, is the fissure of Eolando, or Central fissure,^ which extends upward and backward almost to the great longitudinal fissure. Its upper extrem- ity is about half an inch behind the middle of a line drawn from the nasal eminence to the external occipital protuber- (5) Fissurse interlobulares. (7) Sulcus centralis. (6) Fissura lateralis cerebri. THE CEREBRUM. II ance (the sagittal meridian). With this line the fissure of Rolando forms an anterior angle of 67 to 73 degrees. The fissure of Rolando forms the boundary between the frontal and the parietal lobe. It is developed in two parts, superior and inferior, which join at an angle open backward, the genu, and both parts may present an anterior concavity. (3) Parieto-occipital Fissure.^ — If the line locating the horizontal limb of the fissure of Sylvius be extended back to the sagittal meridian its posterior end marks the location of the parieto-occipital fissure (external part). The greater part of this fissure is on the internal or medial surface of the hemisphere. To the extent of half an inch the external parieto-occipital fissure separates the parietal and occipital lobes from each other. LOBES AND CONVOLUTIONS OP THE CONVEX SURFACE. (I) The Frontal Lobe^ comprises the anterior polar region of the hemisphere back to the Rolandic and the Sylvian fis- sure. It is subdivided by three sulci: The precentral sulcus^^ (superior and inferior parts), which is parallel with the fissure of Rolando (central), and the superior and infe- rior frontal sulci.^i ^he two latter extend downward and forward from superior and inferior precentral sulci, respec- tively, and separate from each other the superior, middle and inferior frontal convolutions.^^ The ascending frontal con- volution^^ (precentral) lies between the precentral sulcus and the fissure of Rolando. It is joined to the ascending parietal convolution^^ (postcentral) by the paracentral lobule,^* (8) Sulcus occipito-parietalla. (9) Lobus frontalis. (10) Sulcus prsecentralia. (II) S. frontalis superior. Inferior. ^ (12) Gyrus frontalis superior, medius. Inferior. (13) G. centralis anterior, posterior. (14) Lobulus paracentralis. 12 THE BRAIN AND SPINAL CORD. above the central fissure, and by the fronto-parietal opercu- lum, below it. The fronto-parietal operculum and posterior part of the inferior frontal gyrus constitute the region of speech. In the foot (posterior end) of the middle frontal gyrus is the writing center (Gordinier). (2) The Parietal Lobe^^ is situated behind the fissure of Eolando and above the horizontal limb of the Sylvian fissure. From the posterior end of the latter to the external parieto- occipital fissure, the lobe is separated from the temporal, below, and the occipital, behind, by an imaginary line. The sulci of this lobe are the intraparietal,^ ^ with an anterior and a posterior ramus (joined by the genu) which are par- allel with the central, and the great longitudinal fissures, respectively; and the postcentral sulcus,^^ which ascends from the genu of the intraparietal almost to the great longi- tudinal fissure. The anterior limb of the intraparietal fis^ sure and the postcentral sulcus separate the ascending pa- rietal convolution^^ from the superior parietal and inferior parietal.^ ^ The posterior limb of the intraparietal fissure separates the superior and inferior parietal convolutions from each other. Indefinite sulci subdivide the inferior parietal into supra-marginalj^^ angular J^^ and postparietal gyri, which wind over the upturned ends of the Sylvian and first and second temporal sulci, respectively. The best known motor areas of the cortex are contained in the ascending frontal, ascending parietal and superior parietal gyri ; in the foot of the inferior and middle frontal convolutions; in the quad- rate and paracentral lobules, and in the marginal gyrus. (15) Lobus parietalis. (16) Sulcus interparietalis. (17) S. postcentralis. (18) Gyrus centralis posterior. (19) Lobulus parietalis superior, inferior. (20) Gyrus supramarginalis. (21) Gyrus angularis. THE CEREBRUM. I 3 The area of general sensation, somcesthetic area/^^ nearly coincides with the great motor areas; it is a little more ex- tensive as it includes much of the limbic lobe. (3) Occipital Lobe.^s — It forms the posterior pole of the hemisphere. With the parietal and temporal lobes it is di- rectly continuous, being marked off from them by an imag- inary line drawn from the preoccipital notch to the external parieto-occipital fissure. The parieto-occipital fissure bounds it to the extent of half an inch; rarely, the external perpen- dicular fissure bounds it in front. Its sulci^* and convolu- tions vary much ; usually the following are found : The su- perior occipital sulcus, vertical, or longitudinal, in direction, and the middle and inferior,^* which are horizontal, divide the lobe into superior, middle and inferior convolutions.^^ The superior occipital sulcus is often continuous with the in- traparietal fissure. The inferior occipital sulcus follows the lower border of the convex surface. The superior and infe- rior convolutions form the corresponding borders of the lobe and trend toward the occipital pole. The middle occipital gyrus is in the angle between them and may reach the medial border. The visual memory center is located in the convex surface of the occipital lobe and in the angular gyrus. (4) The Temporal Lobe^e is that part of the cerebral hemi- sphere behind the main stem and below the horizontal limb of the fissure of Sylvius. It rests in the middle fossa of the skull; and is probably the seat of the centers of taste, smell and hearing. The first temporal sulcus^'^ (or parallel sulcus) and the second temporal sulcus^^ divide the lobe into three (22) Soma—hody—Aesthesis—iterce^tiojh, or feeling. (23) Lobus occipitalis. (24) Sulci occipitales laterales. S. oc. transversus. (,2S) Gyri occipitales laterales. (26) Lobus temporalis. (27) Sulcus temporalis superior, medius. 14 THE BRAIN AND SPINAL CORD. horizontal convolutions, named, from the Sylvian fissure downward, the first, second and third temporal convolutions.^^ In the third and fourth fifths of the first temporal convolu- tion, and in the transverse temporal gyri, concealed in the fissure of Sylvius, is the receptive center of hearing (Barker). Annectant convolutions are small links joining the greater gyri. The first annectant joins the superior parietal and su- perior occipital convolutions. To the middle occipital gyrus, the angular or postparietal is linked by the second annectant and the middle temporal by the third. The fourth annectant unites the inferior temporal and inferior occipital convolu- tions. There are other less constant annectants. (5) The Island of Reil29 is also called the central lobe. Situated within the fissure of Sylvius, it is bounded at the base of the brain by the sulcus limitans insulae (anterior, external and posterior) .^o The sulcus centralis insulae di- vides it into anterior and posterior lohule, each of which is composed of from two to four convolutions.^^ The fronto- parietal operculum and inferior frontal convolution, together with the temporal lobe, cover the insular convolutions, hence the name, gyri operti, also applied to thein. FISSURES OF THE MEDIAL AND TENTORIAL SURFACE. The middle third of this surface^^ fg made by sagittal sec- tion through the connecting links of the hemispheres and the inter-brain. The free surface presents six fissures. (1) Calloso-marginal Fissure. — Beginning under this mid- dle cut surface and extending forward, upward and backwanl until it half encircles the corpus callosum; and then tum- (28) Gyrus temporalis superior, medius, inferior. (29) Insula. (30) Sulcus circularis (Reili). (31) Gyri insulae— G. breves, Gyrus longus. (32) Facies medialis. THE CEREBRUM. 1 5 ing upward to the convex border and ending just behind the fissure of Rolando, is the calloso-marginal fissure.^^ It sep- arates the gyrus fornicatus and the marginal convolution from one another by its anterior part; and, by its upturned posterior end, separates the paracentral lobule from the quad- rate lobe. (2) The Parieto-occipital Fissure (internal part)^* ex- tends upward and backward from just beneath the thick pos- terior margin of the corpus callosum, the splenium, to the border of the medial surface, where it is continuous with the external parieto-occipital fissure. It is situated between the quadrate and the cuneate lobe. (3) Calcarine. — From near the middle of the parieto- occipital, the calcarine fissure^^ extends in a curve downward and backward between the cuneate lobe and the fifth temporal (lingual) convolution and ends bifid. The anterior part of the parieto-occipital fissure, in its formation, may be com- mon either to that fissure or to the calcarine, (4) Hippoeampal Fissure. — A crescentic fissure, convex downward, winds from the splenium of the corpus callosum forward beneath the optic thalamus nearly to the end of the temporal lobe, where it is closed by the uncus. It is the den- tate or hippoeampal fissure.^^ On the surface of the temporal lobe this fissure appears to be identical with the temporal extension of the great transverse fissure, the choroid fissure; but, deeply, it lies posterior to it and is separated from the choroid fissure^"^ by the fascia dentata. (5) Choroid Fissure. — It is of horseshoe shape and extends from the foramen of Monro backward, — ^and downward, — and forward to near the pole of the temporal lobe. On its con- (88) Sulcus cinguli. (36) F. hippocampi. (34) S. parieto-occipitalls. (37) Fissura choroldea. (35) Fissura calcarina. l6 THE BRAIN AND SPINAL CORD. vexity it is bounded by the fornix. The fissure is a com- plete one, involving the whole hemisphere wall. A single lajer of epithelium separates it from the lateral ventricle. The pia mater, dipping into it, forms the choroid plexus of that ventricle. The fissure is again peculiar in the fact that between the roof of the third ventricle and the fornix it is directly continuous with the same fissure on the opposite side. In this antero-superior part, which is in direct continuity with the great transverse fissure, is the velum interpositum. (6) The Collateral Fissure^s is situated below the dentate, parieto-occipital and calcarine fissures, and is developed in three parts. The collateral fissure bounds, inferiorly, the hip- pocampal and the fifth temporal convolution; and separates them from the fourth temporal (fusiform) gyrus. LOBES AND CONVOLUTIONS OF MEDIAL AND TENTORIAL SUR- FACE. They form two concentric rings, interrupted antero-infe- riorly at the vallecula Sylvii, which encircle the corpus cal- losum and optic thalamus. The two rings are separated from one another by a broken fissure, the limbic -fissure, made up of the calloso-marginal (except its posterior end), the post-limbic sulcus, and the anterior part of the parieto- occipital and collateral fissures. Central Ring. — The gyrus fornicatus^^ and hippocampal convolution'^^ joined by the isthmus,*^ at the posterior border of the corpus callosum, form the central ring. The former begins under the corpus callosum in the frontal lobe anterior to the fissure of Sylvius; and the latter terminates as uncus just behind that fissure in the temporal lobe. The central ring forms the chief part of the limbic lobe. (38) Fissura collateralls. (40) Gyrus hippocampi. (39) Gyrus cinguli. (41) Isthmus gyri fornicati. THE CEREBRUM. I 7 The Peripheral Ringf, from before backward, is composed of the marginal convolution ^'^^ ending in the paracentral lohule^^; the quadrate lohej^^ bounded anterio-inferiorly by the postlimbic sulcus; the cuneate lohe^^j the fifth tempo- ral convolution (infracalcarine, or lingual) ^^; and the fourth temporal, or fusiform, convolution^'^ A slight sulcus (third temporal) separates the last from the third temporal gyrus on the convex surface. The quadrate and paracentral lob- ules and the posterior third or half of the marginal gyrus contain motor centers, for the opposite side of the body, the head, arm, trunk and leg centers being located in this order from before backward. The uncinate convolution is the combined hippocampal and fifth temporal gyri. Limbic Lobe. — It is composed of the following parts, viz. : (1) The gyrus fomicatus and hippocampal convolution; (2) the nerves of Lancisi and peduncle of the corpus callosum; and (3) the pillars and half the body of the fornix, one-half of the septum lucidum, and the fascia dentata. It is encir- cled by the limbic fissure. The limbic lobe probably con- tains the centers of smell and taste, which are localized in the hippocampal gyrus and uncus. Together with the olfactory lobe it constitutes the Rhinencephalon. BASAL OR INFERIOR SURFACE. The basal surface of the cerebrum^^ comprises the inferior surface of the hemispheres and of the inter-brain. It ex- tends from the anterior poles of the hemispheres back to the fissure of Sylvius, laterally; and, in the median line, to the (42) Gyrus frontalis superior. (46) Gyrus lingualis. (43) Lobulus paracentralis. ■ (47) Gyrus fusiformis. (44) Prsecuneus. , (48) Facies basalis cerebri. (45) Cuneus. j) I8 THE BRAIN AND SPINAL CORD. posterior perforated lamina and crustse of the mid-brain. The great longitudinal fissure splits it into lateral halves in front, separating the frontal lobes of the cerebrum from each other. The fissure extends back to the upturned part (lamina ter- minalis) of the lamina cinerea and to the corpus callosum. The length of the fissure is considerably less than one-third of the cerebral axis. The medial structures of this surface, named from before backward, are as follows: Lamina cinerea. Optic chiasm, or optic commissure, Tuber cinereum. and infundibulum. Pituitary body. Corpora albicantia. These are often called interpeduncular structures. Con- stituting the hase of the inter-hrain, they form a continuous sheet beneath the third ventricle and optic thalami, which joins, antero-laterally, the anterior perforated lamina and the cortex of the internal orbital convolution. The Lamina Cinerea is the most anterior of the medial structures. It is a thin lamina of ash-colored (cinereum) gray matter. Arching from behind forward over the supe- rior surface of the optic commissure to which it is attached, it then turns upward and backward, the reflected part con- stituting the lamina terminalis, and meets the rostrum of the corpus callosum. In the angle of turning is the optic recess. The lamina terminalis, which is seen in the floor of the great longitudinal fissure, forms part of the anterior boundary of the third ventricle. Tuber Cinereum. — At the posterior border of the optic commissure, the lamina is continuous with the tuber cine- reum. Here the gray matter is thickened and centrally prom- THE CEREBRUM, I9 inent. The bulbous infundihulum projects downward from it to rest in the sella Turcica, where it forms the posterior lobe of the pituitary body. The upper half of the infundih- ulum is hollow (funnel-like). Its cavity forms the lowest part of the third ventricle. In man the bulb of the infundib- ulum is solid at maturity, though hollow in the embryo. It is composed largely of fibrous tissue, notwithstanding the fact that it is developed from the floor of the Thalmencephalon. From the base (superior end) of the infundihulum, the tuber, cinereum extends in continuity with the anterior perforated lamina and hypothalamic gray matter on each side of it; and, behind, the corpora albicantia mark the boundary between it and the posterior perforated lamina of the mid-brain. The lamina cinerea and tuber cinereum form the inferior, or great, gray commissure of the inter-brain. The Pituitary Body (hypophysis) is composed of two lobes bound together by connective tissue. A sheet of dura mater (diaphragma sellae) holds them in the pituitary fossa. The anterior lohe, the larger, is derived from the epithelium of the mouth cavity; and, in structure, resembles' the thyroid gland. Its closed vesicles, lined with columnar epithelium (in part ciliated), contain a viscid jelly-like material (pitu- ita), which suggested the name for the body. The anterior lobe is hollowed out on its posterior surface (kidney-shape) and receives the posterior lobe, the infundihulum, into the concavity. The pituitary body appears to have an inhibitive action on growth and is found diseased in acromegalia. Corpora Albicantia. — Two white bodies, as large as a small pea, the corpora albicantia,^^ are situated one on either side of the median line, between the tuber cinereum and the pig- mented gray matter of the posterior perforated lamina. Each (49) Corpora mamillaria. 20 THE BRAIN AND SPINAL CORD. is formed by a loop in the anterior pillar of the fornix and is, therefore, composed of white fibers on the surface. There is gray matter in the interior, which may contain the ends of the fornix fibers and be the seat of origin of the ascending bundle, the bundle of Vicq d'Azyr.^<* The latter terminates in the optic thalamus. (Note 14, page 226.) Immediately behind the corpora albicantia is the posterior perforated lamina. This is the exposed part of the substan- tia nigra of the mid-brain, perforated for the passage of the postero-median ganglionic arteries to the optic thalami and walls of the third ventricle. The pons and crustse bound it behind. Issuing from the inner side of the crusta^^ is the large motor oculi, or third cranial, nerve^^. qj^^ coursing over its surface from behind forward, is the smaller troch- lear or fourth nerve.^^ The crustae will be described with the mid-brain to which they belong. The Optic Chiasm (chiasma opticum) remains to be de- scribed. It is situated medially beneath the lamina cinerea, in the optic groove of the sphenoid bone. The fibers of the optic nerves and tracts compose it. There are three sets of these fibers, namely, the intercerehral, direct and decussat- ing. A fourth group of fibers, called interretinal and said to be commissural for the retinae, has been hitherto described, but their existence is very doubtful. The intercerehral fibers are not found in the optic nerves, but form a commissure (Gudden's) for the internal geniculate bodies. The direct and decussating fibers run through tract and nerve and join the brain with the retina of the same and of the opposite side, respectively. In most vertebrates below mammals and (50) Fasciculus thalamomamillaris. (51) Basis pedunculi cerebri (sing.). (52) Nervus oculomotorius. (53) N. trochlearis. THE CEREBRUM. 21 in the mouse and guinea pig, the optic fibers all decussate in the chiasm. Normally in man and the higher mammals, the lateral half of each retina receives direct fibers and the medial half crossed fibers. The optic nerves^* extend from the front of the commissure into the orbits through the optic foramina and terminate in the ganglionar cells of the retinae. The optic tracts^^ connect the commissure with the brain. Each tract winds outward and backward around the cerebral peduncle, and divides into an internal and an external root.^^ The roots wind around the optic thalamus and disappear (superficial origin) at the corresponding geniculate body. The fibers of the external root may be traced to the external geniculate body (80 per cent. Von Monokow), to the optic thalamus (nearly all the 20 per cent, remjaining) , and the rest to the anterior quadrigeminal body. The optic radiations of the internal capsule connect these centers with the medial occipital cortex. The internal root rises from the internal geniculate body and optic thalamus. The nuclei of the optic fibers are probably connected with the cerebellum by the fillet. Notice now the hose of the hemispheres, comprising the or- bital and olfactory lobes. Orbital Lobe. — The inferior surface of the frontal lobe, resting on the orbital plate of the frontal bone, is called the orbital lobe.^'' It is separated from its fellow by the great longitudinal fissure, and is bounded behind by the vallecula Sylvii and fissure of Sylvius, overlapped by the tem- poral lobe. More accurately, the posterior boundary is the anterior perforated space and the anterior fissure of Eeil. The orbital lobe is concave transversely aod is divided by a (54) Nervi optlci. (56) Radix medialls, lateralis. (55) Tractus optlci. (57) Lobus orbitalis. 22 THE BRAIN AND SPINAL CORD. Triradiate, or an H-shaped fissure,^^ directed fore and aft, into internal, anterior and posterior orbital convolutions.^^ The internal orbital convolution lies beside the great longi- tudinal fissure, and is continuous with the marginal convolu- tion on the medial surface. Its anterior end joins the supe- rior frontal convolution; its posterior, the trigone and area of Broca. The internal orbital convolution is subdivided by the sulcus olfactorius, which contains the olfactory tract; and that part of the convolution medial to the olfactory fis- sure is called the gyrus rectus. The anterior and posterior orbital convolutions may be traced to the convex cerebral surface in continuity with the middle and inferior frontal If the anterior part of the temporal lobe be removed, the under surface of the island of Eeil is brought into view. The sulcus limitans insulse^^ bounds it on three sides (ante- rior, external and posterior), and separates it from the pos- terior orbital gyrus, in front; the frontal and fronto-parietal opercula, externally; and from the temporal lobe, behind. (See lobes of convex surface.) Olfactory Lobe. — This term includes the remainder of the structures forming the inferior surface of the cerebrum. The reason for calling them the olfactory lobe^^ is found in the lower animals; and in the human embryo, where it exists as a prominent hollow process of the cerebral hemisphere. A constriction (fissura prima) divides this diverticulum into the anterior and posterior olfactory lohule. In the human adult the anterior olfactory lobule is represented by the bulb, the tract, the trigone and the area of Broca. The anterior per- forated lamina (or space) represents the posterior lobule. The Olfactory Bulb^^ is an ovoid mass of brain matter (58) Fissures orbitales. (61) Lobus olfactorius. (69) Gyri orbitales. (62) Bulbus olfactorius. (60) Sulcus circularis (Reili). THE CEREBRUM. 23 about a half-inch long and one-sixth of an inch in diameter. It rests between the orbital lobe and the cribriform plate of the ethmoid bone. Below and on each side, it is composed of cortical gray matter (four layers) from which rise the twenty or thirty olfactory nerves.^^ The nerves, after enter- ing the nasal fossa through the cribriform plate, are distrib- uted to the Schneiderian membrane. The cells of Max Schultze in the Schneiderian membrane are the real cell- bodies of the olfactory nerve fibers (axones), hence the latter grow upward to the bulb. The fibers form the first layer of the bulb, olfactory nerve layer, and arborize about the den- drites of the large mitral cells to form the second layer, — the stratum glomerulosum. In the third layer of the gray matter are found great mitral cell-bodies, whose medullated axis-cylinders, or axones, form the white matter of the bulb ; and, continued backward, constitute the olfactory tract. Olfactory Tract. — The tract^* is triangular in section, nearly an inch long and one line in width. It is concealed in the olfactory sulcus. At its base it divides into external and infernal root,^^ which inclose between them the trigone into which some fibers may be traced, forming the middle root.^^ The external root courses backward and outward and terminates in the uncus at the anterior extremity of the hip- pocampal convolution. It crosses the anterior perforated space. The internal root bends sharply inward, toward the median line, and runs between the trigone and area of Broca. Its fibers turn into Broca^s area and the gyrus fomicatus. Thus the two roots unite the opposite ends of the limbic lobe. From the bifurcation of the olfactory tract, a few fibers pro- ceed into the trigone and frontal lobe. (63) Nervi olfactorii. (64) Tractus olfactorius. (65) Striae olfactorise, lateralis, medialis, intermedia. 24 THE BRAIN AND SPINAL CORD. The Trigone and Area of Broca. — The triangular portion of coi-tex between the inner and outer olfactory roots, called the trigone,^^ is continuous medially with Broca's area.^''' The internal root marks the boundary between them. Both are bounded behind by the fissura prima (transverse part), and the oblique part of the same fissure separates the area of Broca from the peduncle of the corpus callosum. The area of Broca is limited in front by a slight curved depres- sion, the fissura serotina. On the medial surface, Broca's area joins the gyrus fornicatus. Some of the fibers of the middle root of the olfactory tract probably pass through the anterior commissure; and, after piercing the opposite corpus striatum, terminate in the tem- poral lobe. They constitute the only olfactory decussation known. The Posterior Offactory Lohule is identical with the ante- rior perforated lamina.^ ^ It is separated from the trigone by the transverse fissura prima. Internally, it is in direct con- tinuity with the lamina cinerea. The optic tract bounds it, postero-medially. Externally, it forms the floor of the valle- cula Sylvii, where it is overlapped by the temporal lobe. Su- periorly, it is continuous with the base of the corpus striatum. Coursing over the inner and outer border of the anterior per- forated lamina are the callosal peduncle and external ol- factory root, which converge and meet in the hippocampal convolution. The perforations of the lamina are for the antero-lateral ganglionic arteries. Section II. — Interior Surface of the Cerebrum. The boundaries of the cerebral ventricles constitute the interior surface of the cerebrum. Considering all the cere- (66) Trigonum olfactorium. (67) Area parolfactoria (Broca). (68) Lamina perforata anterior. THE CEREBRUM. 2$ bral cavities together, we notice that they occupy a wedge- like space. In shape the wedge is rectangular; and it stands, base upward, against the corpus callosum. Its beveled sur- faces look toward the hemispheres. The blade is driven down- ward as if to split the cerebrum into lateral halves, the edge resting on the medial structures at the base of the brain. The space is inclosed laterally between the diverging internal capsules, which, within the hemispheres, decussate with the lateral extremities of the corpus callosum. The two struc- tures most necessary to an understanding of the cerebral cavity, therefore, are the internal capsule^ and corpus cal- losum. ' Internal Capsule. — Looking at the base of the brain, we see two broad bands of nerve fibers, the crustae,^ issue from the front of the pons and, diverging upward and forward, enter the hemispheres beneath the optic tracts. These peduncular fibers are reinforced by additional fibers within the hemi- sphere. The fibers then radiate toward the cerebral cortex in the form of a hollow cone or funnel. This funnel-like group of fibers is the internal capsule. The bell of the fun- nel opens upward and outward and contains the lenticular nucleus; its solid spout, directed toward the pons and me- dially, is the crusta. Antero^inferiorly the fibers in the bell of the funnel diverge to opposite sides of the fissure of Syl- vius and produce a break in its continuity, the hiatus 8ylvii; otherwise the funnel is complete. As the internal capsule proceeds into the hemisphere, it impales the corpus striatum in such manner as to place the caudate nucleus and amygdala upon its circumference and to inclose within its walls (to capsulate) the lenticular nucleus. The lenticular nucleus is separated externally from the claustrum by a thin layer of fibers called the external capsule.^ (1) Capsula interna. (2) Bases pedunculi. (3) Capsula externa. 26 THE BRAIN AND SPINAL CORD. Inferior Lamina. — -Tlie internal capsule* is flattened from above downward. It has, therefore, a superior and an infe-: rior lamina, which, posteriorly, are continuous with each- other; but, anteriorly, are separated by the fissure of Sylvius.: The inferior lamina (or inferior ramus, as seen in sagittal/ section) is a very thin layer and bevels down to a sharp edge: anteriorly. In front it presents a free border. Its fibers pass outward beneath the lenticular nucleus and, after wind- ing over the amygdala and the descending horn of the lateral ventricle, terminate in the parietal and temporal lobes. Motor Fibers. — It contains part of the Temporo-pontal motor tract which extends from the temporal cortex to the nucleus of the pons. Sensory Fibers. — ^And also the following sensory fibers are found in the inferior lamina, viz., the Ansa Peduncularis (conraionl sensory) running from the thalamus to the som- sesthetic cortex, and part of the Aciistic Eadiations (special sensory) which ext^snd from the internal geniculate body to the auditory cortex in the superior and transverse tem- poral gyri. In the angle between the descending horn and the body of the lateral ventricle, the inferior lamina joins the superior. The Superior Lamina (or superior ramus) of the internal capsule contains most of the crusta. It is a thick and strong sheet of fibers. Often it is considered as identical with the "internal capsule,'^ the inferior lamina being disregarded. The superior lamina ascends, fan-like, from the crusta to the lateral extremity of the corpus callosum, with which it in- tercrosses. It has a free border anteriorly, though imbedded in the corpus striatum. Upon its internal surface rest the optic thalamus, below and behind, and the caudate nucleus, above and farther forward. It thus separates the optic thala- (4) Capsula Interna. ' . :^ i : THE CEREBRUM 2/ mus and caudate nucleus from the lenticular nucleus. A bend near the middle of the superior lamina, called the genUj divides it into an anterior^ and a posterior segment,^ which tend slightly outward from the genu and form an angle with each other, open outward, of about 120 degrees. Motor Fibers. — The fibers of the genu of the internal cap- sule are very largely motor and constitute the Pyramidal Tract. They may be traced from the Eolandic area of the cortex, through the genu of the internal capsule and middle three-fifths of the crusta, and on down into the spinal cord, where they end in ramifications about the cell-bodies in the anterior horn of gray matter. From these same spinal cell- bodies other fibers rise which constitute the motor part of the spinal nerves. Fibers of the pyramidal tract also end in the mid-brain pons and medulla: their end-tufts are related to the nuclear cell-bodies of motor cranial nerves. The anterior segment (pars frontalis) of the internal capsule contains a motor tract which extends from the prefrontal cortex through the inner one^fifth of the crusta to the nucleus of the pons and motor nuclei of cranial nerves (Flechsig). It is the Fronto-pontal Tract."^ In the posterior segment (pars occipi- talis), behind the pyramidal tract, and also partly in the inferior lamina, is another motor tract, described by Flechsig. It rises from the temporal cortex and running beneath and behind the lenticular nucleus and through the outer one-fifth of the crusta, terminates in the nucleus of the pons, and also in nuclei of motor cranial nerves (Spitzka). That is the Temporo-pontal Tract.^ Sensory Fibers. — In both segments of the internal capsule there are oommon sensory fibers which rise chiefly in the (5) Pars frontalis. (6) Pars occipitalis. (7) Traotus cerebro-corticopontalis frontalis. (8) T. cerebro-corticopontalLs temporalis. 28 THE BRAIN AND SPINAL CORD. optic tlialamus and end in the somaesthetic cortex. They constitute the Cortical Fillet and convey ordinary sensations. In the anterior segment is the Anterior Stalk of the Thal- amus which ends in somaesthetic cortex anterior to the pre- central fissure. The posterior segment contains the Ansa Lenticularis, which conveys ordinary sensations from the thalamus to the somaesthetic cortex chiefly in the upper Eo^ landic area. At the junction of the superior and inferior laminsB of the internal capsule are. the special sense fibers. The Optic Eadiations^ and Auditory Eadiations^^ occupy the retro-lenticular part of the internal capsule. The former ex- tend through it from the optic thalamus and external genicu- late body to the cuneus; the latter rise in the internal genic- ulate body and end in the superior and transverse temporal convolutions. Many fibers of the internal capsule give off branches (collaterals) which pass through the corpus callo- sum to the opposite hemisphere; other fibers may be traced entire through the same course to the cortical cells of the op- posite side. (For fibers of inferior lamina see page 26.) The superior lamina of the internal capsule, proceeding outward and upward into the hemisphere, decussates with the corpus callosum and enters into the corona radiata. To- gether with the caudate nucleus, optic thalamus and tsenia semicircularis, which lie on its internal surface, it forms the entire lateral boundary of the general cavity of the cerebrum. It thus determines the lateral part of the interior cerebral surface. Corpus Callosuin. — The entire roof of the cerebral cavity, representing the base of the wedge, is formed by the corpus callosum. A part of the anterior boundary is also formed by it. The corpus callosum is a thick sheet of fibers four (9) Radiatio occipito-thalamica (Gratioleti). (10) Radiatio temporothalamica. THE CEREBRUM. 29 inches broad, from before backward, which joins the hemi- spheres together. It constitutes the great white commissure, being composed chiefly of those medullated cortical axones which end in arborizations about cortical cells of the opposite hemisphere. It contains some fibers which, after passing through it, turn down in the internal capsule; and, also, col- laterals from capsular and association fibers. The corpus callosum is placed nearer to the anterior than the posterior pole of the hemispheres. Separating the hemispheres above, it is seen in the bottom of the great longitudinal fissure. It is about an inch in transverse length. The upper surface is concave from side to side; and di- vided, medially, by a longitudinal raphe. Transverse striae are plainly visible. A few longitudinal stria are also found running on either side of the raphe, the nerves of Lancisi^^ ; and others run near the lateral end of the callosum.^ ^ At the anterior and at the posterior border, the corpus callosum is bent downward (scroll like) ; hence, it is superiorly convex from before backward. Its inferior surface is concave antero-posteriorly and near its posterior border is fused with the body of the fornix. Anterior to that fusion, it is joined to the fornix, along the median line, by the septum lucidum. The posterior l order is flexed downward about forty-five degrees. Giving passage to the fibers which join the middle and posterior parts of the hemispheres, the posterior border is the thickest part of the corpus callosum. It is on that ac- count called the pad, or splenium. The anterior border is bent downward and then backward, sweeping through 180 degrees of flexion. It terminates in a sharp edge (sharp point, seen in sagittal section) called the (11) striae longitudinales mediales et laterales. 30 THE BRAIN AND SPINAL CORD. rostrum. The rostrum is continuous with, the lamina termi- nalis at the base of the brain. It sends downward on either side a band of fibers, continuous with the nerves of Lancisi, which constitutes the peduncle of the corpus callosum. Each peduncle, after passing across the anterior perforated lamina, ends in the uncus of the hippocampal gyrus. The transverse fibers of the rostrum, in the hemisphere, form the floor of the anterior horn of the lateral ventricle. Genu and Truncus. — The down-turned part of the corpus callosum is the genu. It joins the rostrum to the main body, the truncus. The genu forms part of the anterior boundary of the cerebral cavity; the truncus forms the roof. Fibers uniting the frontal lobes of the 'cerebrum pass through the genu, and in the hemisphere, bound the anterior horn of the lateral ventricles above and in front. Those fibers arching forward and forming the roof of the anterior horn are called the forceps minor. The forceps major, composed of fibers from the splenium which bend backward into the occipital lobe, lies in the roof and inner wall of posterior horn. Each lateral extremity of the corpus callosum is overhung by the gyrus fomicatus, which covers the lateral longitudinal striae (taeniae tectae).^^ Inclosed between the gyrus fomicatus and corpus callosum is the fissure-like ventricle of the callo- sum, which represents part of the fissura prima of the embryo. Under the splenium the fissura prima is continued in the hip- pocampal fissure. The boundaries of the general cavity of the cerebrum may be given as follows: Roof (base of wedge) — Corpus callosum. (12) striae longitudinales laterales. THE CEREBRUM. 31 Floor (edge of wedge) — Tegmentum (Mid-brain), Posterior perforated lamina (Mid-brain), Tuber cinerenm, Infundibulum, Lamina cinerea. ! Lateral wall (beveled surface) — Internal capsule. Caudate nucleus. Taenia semicircularis, Optic thalamus. ' Anterior wall (border of wedge) — Lamina terminalis. Anterior commissure. Genu of corpus callosum. ; Posterior wall — Corpora quadrigemina (Mid-brain) and Posterior commissure (with aqueduct of Sylvius beneath them). Pineal body, Grreat transverse fissure, containing the velum interposi- tum, Splenium (being bent down slightly behind the cavity). The cerebral cavity thus bounded is subdivided by two partitions. The body of the fornix, together with the velum interpositum and roof epithelium of the third ventricle, forms a horizontal partition which divides the cavity into an upper and lower chamber. The superior chamber is divided into two lateral chambers, the lateral ventricles, by a double ver- tical partition, the septum lucidum. The inferior chamber is the third ventricle. 32 THE BRAIN AND SPINAL CORD. The body of the fornixes jg ^ triangular sheet of fibers, whose base is attached to the under surface of the splenium of the corpus callosum, and whose bifid apex extends forward to the rostrum and to the anterior commissure. Its lateral borders rest on the optic thalami, the velum interpositum alone intervening. And the narrow chamber between the optic thalami (the third ventricle) is separated from the broader, superior part of the cerebral cavity by the body of the fornix. The bo^dy of the fornix is produced by the ap- proximation of two bundles of white fibers, one belonging to each hemisphere. These bundles are the pillars of the fornix. The posterior pillar^^ may be traced from the uncus (as corpus fimbriatum), and from the hippocampus major, its chief origin, upward through the descending horn and into the floor of the body of the lateral ventricle, where it unites with its fellow of the opposite side in forming the body of the fornix. At the apex of the body of the fornix, which is the anterior end, the bundles again separate and become the anterior pillars. The posterior pillars are united at the back part of the body of the fornix by a few transverse and oblique fibers which form the lyre, or commissura hippocampi. The commissure is best seen when the corpus callosum and fornix are viewed from below ; its fibers connect each posterior pillar of the fornix with the optic thalamus, hippocampus major and uncus of the opposite side. The anterior pillars ^^ one on either side, pass down in front of the optic thalami, bounding the foramina of Monro; and then descend to the corpora albicantia, at the base of the brain. On the way down the pillars pass behind the anterior (13) Corpus fornicis. (14) Crus fornicis. (15) Columnse fornicis. THE CEREBRUM. 33 commissure, beyond which each pierces the inner part of the optic thalamus of the same side. The fibers of the anterior pillars probably terminate in the corpora albicantia, from which other fibers take their origin (the bundles of Vicq d^Azyr)^^ and ascend to the anterior nuclei of the optic thalami. The up'per surface of the body of the fornix is convex from before backward. It forms the postero-median part of the floor of the lateral ventricle. Medially, it is joined to the corpus callosum by the septum lucidum.^"^ The septum lucidum, a double-walled sagittal partition, divides the superior chamber of the cerebral cavity into lateral halves, the lateral ventricles. The septum lucidum is cres- centic in outline. Its convex border fits, medially, into the concave surface of the body, genu and rostrum of the corpus callosum. Its concave border rests upon the fornix. Each wall of the septum lucidum is a part of the original medial wall of the cerebral hemisphere and is, therefore, composed of cortical and medullary matter. The walls inclose a part of the great longitudinal fissure, called the fifth ventricle. That fissure, in embyro, was open down to the velum inter- positum on the inter-brain; but its lower part becomes cut off and inclosed by the development of the fornix, anterior commissure and corpus callosum. The cerebral cavity is thus divided into four ventricles, viz. : Two lateral (the ventricles of the hemispheres), Fifth (the ventricle of the great longitudinal fissure), and Third (ventricle of the inter-brain). THE FIFTH VENTRICLE. This is the fissural ventricle, or the ventricle of the sep- (16) Fasciculus thalamo-mamlllarls. (17) Septum pellucidum, , , J 34 THE BRAIN AND SPINAL CORD. tum.^^ The fifth ventricle is a very narrow, anteroposterior cleft between the walls of the septum lucidum, with which it coincides in extent. It is situated within the concavity of the corpus callosum between the lateral ventricles, above and anterior to the third ventricle. Below and posteriorly it is bounded by the fornix. It is not a part of the embryonic brain cavity, but of the great longitudinal fissure. There- fore it does not communicate with any other ventricle, each of the others being a part of the cavity of the neural tube from which both brain and cord are developed. Instead of ependyma, which lines other ventricles, the lining of the fifth is modified pia mater. A lymph-like fluid fills it. THE LATERAL VENTRICLE. The hemispheres contain the largest of the six ventricles. Situated one on either side of the median line, the ventricles of the hemispheres are very naturally called the lateral ventricles.i^ Each represents a branch of the cavity of the embryonic neural tube. In consequence, the lateral ventricles communicate with all others except the fifth. By the fora- men of Monro, each directly communicates with the third ventricle; and through that, indirectly, with the fourth and sixth. The foramen of Monro^o is situated between the front of the optic thalamus and the anterior pillar of the fornix. It extends between the anterior extremity of the third ven- tricle (the aula) and the junction of the anterior horn with the body of the lateral ventricle. The lateral ventricles are lined with ependyma, which is a transparent membrane com- posed of two layers, viz., neuroglia, with a covering of columnar ciliated epithelial cells. Over the optic thalamus (18) Cavum septl pellucldl. (19) Ventriculi laterales. (20) Foramen interventriculare (Monroi). THE CEREBRUM. 35 (the part seen in the lateral ventricle) and the choroid plexus, the neurogliar layer is absent. The lateral ventricle may be studied best in four parts: the central part or body ; the anterior, the middle or descend- ing, and the posterior comu. The body of the lateral ventricle^i is the ventricle of the parietal lobe of the cerebrum. The following are its bound- aries : Eoof — Corpus callosum. Floor (from before, backward and inward) — Caudate nucleus of the corpus striatum. Taenia semicircularis. Optic thalamus (covered by epithelium). Choroid plexus (covered by epithelium), Fornix. Medial wall — Septum lucidum. External wall — Internal capsule. The corpus callosum forms a complete roof for the body of the lateral ventricle. The roof inclines upward and out- ward from the septum lucidum, the inner wall of the ven- tricle, to the superior lamina of the internal capsule, which forms its outer wall. The floor of the body of the ventricle is formed by the five parts, as named above, which will now be considered in the order given. Corpus Striatum. — The striated body is the basal ganglion of the hemisphere. It is an ovoid mass of gray matter im- bedded, for the most part, in the cerebral medulla; but it is continuous below with the anterior perforated lamina and extends above into the floor of the lateral ventricle. It meas- ures two inches from before backward, an inch and a quarter transversely, and, from above downward, one inch and a half. (21) Ventriculus lateralis (pars centralis). 36 THE BRAIN AND SPINAL CORD. It is placed anterior and external to the optic thalamus. It is a reddish-gray body and the streaked appearance of the corpus striatum is due to the white capsular fibers which pierce it. The striated body is an important way-station in the motor conduction path and perhaps one of less impor- tance in the sensory path. The internal capsule divides it into two nu.clei, namety, the lenticular nucleus (extra ven- tricular part) ,22 and the caudate nucleus, which is seen in the lateral ventricle. Anterior to the free borders of the superior and inferior capsular laminae, the two nuclei are united with each other, with the anterior perforated lamina and with the lower end of the claustrum. The Lenticular Nucleus occupies the cone-like cavity of the internal capsule, by whose laminae it is separated from the ventricle. It is shorter fore and aft than the caudate nu- cleus. It resembles a biconvex lens with a somewhat thick- ened anterior border, when viewed in horizontal section. In transverse vertical section through its center, it is triangular in shape. The hypotenuse and base are formed, respectively, by the superior and inferior laminae of the internal capsule. The external capsule forms the perpendicular anid separates the lenticular nucleus from the claustrum. The latter is a thin sheet of isolated gray matter, found just medial to the island of Reil. In extent and position, fore and aft, the island of Eeil and lenticular nucleus coincide. The lenticu- lar nucleus is subdivided by two white laminae, parallel with its external surface, into three zones. The outer zone, called the putamen, is deeply pigmented, and, like the caudate nucleus, is of a reddish-gray color; but the two inner zones, having less pigment, are of a pale yellowish tint. They form the globus pallidum. The Nucleus Caudatus (the tailed nucleus) is a pear-shaped (22) Nucleus lentiforxnls. THE CEREBRUM. 37 body of reddisli-gray color, situated on the perimeter of the internal capsule. It is the intra- ventricular part of the striated body and forms a strip of the ventricular floor along the outer wall. The hulh^^ of the caudate nucleus is directed forward. It is seen in the anterior horn of the lateral ven- tricle. From the bulb the nucleus tapers as it proceeds back- ward through the body of the ventricle. Its tail, or sur- cingle,^'^ turns downward in the roof of. the middle horn, and ends in a considerable swelling, called the amygdalaj^^ near the apex of the horn. The caudate nucleus is covered on its ventricular surface by ependyma. The opposite surface, resting against the fibers of the internal capsule, is irregular and serrated. The Taenia Semicircularis^^ lies just internal to the nucleus caudatus. It is a band of white fibers traversing the floor of the body of the ventricle and the roof of its descend- ing horn, but covered by the vein of the striate body. It may be said to rise from the amygdala. Ascending to the ventricle, it passes forward between the caudate nucleus and the optic thalamus to the foramen of Monro, where it divides into two bundles. One of them joins the anterior pillar of the fornix. The other, passing over the anterior commissure, terminates in front of it in a mass of cells between the septum lucidum and the nucleus caudatus. Perhaps some fibers terminate in the latter. Optic Thalinus.27 — A fusiform part of this ganglion of the inter-brain is visible in the floor of the lateral ventricle, between the taenia semicircularis and the choroid plexus. It extends throughout the ventricular body from the foramen of Monro to the descending horn. A transparent layer of (23) Caput nuclei caudatl. (26) Stria terminalis. (24) Cauda nuclei caudati. (27) Thalamus. (25) Nucleus amygdalse. 38 THE BRAIN AND SPINAL CORD. epithelium, extending from the fornix to the tsenia semi- circularis, and representing the hemisphere wall, covers it. The optic thalamus will be described with the third ventricle and inter-brain. The Choroid Plexuses of the lateral ventricle is the vascular border of the velum interpositum. It projects, laterally, from beneath the fornix and its posterior pillar into the floor of the body of the ventricle and the inner wall of the descending horn. The epithelium, above mentioned, invests it; and it borders the fornix like a ruffle. It is called choroid plexus (chorion^ a membrane) because it is membrane-like. The anterior choroid artery^^ from the internal carotid and the postero-lateral choroid, a branch of the posterior cerebral, sup- ply the plexus. The former pierces the temporal lobe and en- ters the apex of the descending horn of the ventricle; the latter passes in through the great transverse and choroid fissures, following the velum interpositum. The choroid vein carries the blood away. At the foramen of Monro, it is joined by the vein of the striated body and forms the vein of Galen. The vein of Galen^^ courses backward in the velum inter- positum and unites with its fellow of the opposite side; and then the common vein of Galen,^^ uniting with the inferior longitudinal sinus, forms the straight sinus. The floor of the body of the lateral ventricle is completed by the superior surface of the fornix. The comua^^ Qf i}^q lateral ventricle are three in number. The anterior cornu^^ projects from the body of the ven- tricle forward and outward around the bulb of the caudate (28) Plexus choroideus ventriculi lateralis. (29) Arteiia choroidea anterior. (30) Vena cerebri interna. (31) V. cerebri magna (Galeni). (32) Cornua ventriculi lateralis. (33) Cornu anterius ventriculi lateralis. THE CEREBRUM. 39 nucleus. It is the ventricle of the frontal lobe and is deep and narrow. Its boundaries are as follows: Koof — Corpus callosum (forceps minor). Floor — ^Eostrum. Anterior wall — Genu. Inner wall — Septum lucidum. Outer wall — Caudate nucleus. The posterior cornu^* is directed backward and downward in a curve concave inward, from the ventricular body into the occipital lobe. Its extremity bends medially toward the calcarine fissure, with which the horn is parallel. That fissure produces the ridge along the inner wall called the hippo- campns minor.^^ The posterior horn is roofed over by fibers from the splenium of the corpus callosum, which turn down outside the horn and also form part of the external boundary. A well-marked bundle of fibers from the splenium, forceps major, is found passing along the medial border of the roof into the occipital lobe. The white matter of the occipital lobe forms the remaining boundaries. The anterior extrem- ity of the posterior cornu is continuous, laterally, with the beginning of the descending horn. At the junction of the two is a triangular area, the trigonum ventriculi. The middle, or descending, cornu^^ is the ventricle of the temporal lobe. Its course is crescentic as it follows the peri- meter of the internal capsule. It first runs outward arid backward from the body of the ventricle, then it turns down- ward, and finally it proceeds forward and inward to within an inch of the apex of the temporal lobe. In horizontal sec- tion just below the general cavity of the ventricle, the de- scending horn is triangular. In that position it has a poste- rior wall or floor, an inner wall, and a curved antero-external (34) Cornu posterius ventriculi lateralis. (35) Calear avis. (36) Cornu inferius ventriculi lateralis. 40 THE BRAIN AND SPINAL CORD. wall or roof, which is continuous above with the outer wall and floor of the body of the ventricle. The parts found in the walls of the descending comu may be enumerated as follows : Eoof (or antero-extemal wall) — Pulvinar of optic thalamus (covered by epithelium). Inferior lamina of internal capsule, partially covered by surcingle and amygdala of caudate nucleus, and taenia semicircularis. Floor (or posterior wall) — Eminentia collateralis, Hippocampus major and pes hippocampi, Posterior pillar of fornix and corpus fimbriatuni. Inner wall (medial) — Epithelium (of hemisphere wall) covering, Pulvinar, Choroid plexus, Choroid fissure, and Dentate fascia. The structures in the roof of the descending horn have been sufficiently described. They are easily understood when it is recalled that the roof of the horn is continuous with the outer wall and floor of the ventricle; the internal capsule (inferior lamina), the surcingle and amygdala and the taenia semicircularis form it. Beginning at the trigonum ventricuW^ and extending along the outer border of the floor to the end of the descend- ing horn is a low ridge caused by the collateral fissure. It is the eminentia collateralis. In front of it and internal to it is a prominent ridge, the hippocampus major,^^ which en- (37) Trigonum collaterale. (38) Hippocampus. THE CEREBRUM. 4I larges downward to a lobulated extremity, called the pes hippocampi.^^ Tlie ridge is due to the infolding of the floor over the hippocampal fissure on the medial surface of the cerebrum. The ventricular surface of the hippocampus major is formed by a lamina of white matter, the alveus, but the deeper part is cortical matter composed almost entirely of pyramidal cell-bodies. The posterior pillar of the fornix rests in the concavity of the hippocampus, where most of its fibers originate, but a small bundle of them, the corpus flmbriatum, passes beyond it to its origin in the uncus. A layer of epithelium, representing the hemisphere wall, forms the floor of the choroid fissure and the whole inner wall of the descending cornu. It covers the cushion-like projection (the pulvinar) of the optic thalamus, which forms a small part of both roof and inner wall. Behind and su- periorly, it is attached to the pillar of the fornix, from which it extends forward and outward to the taenia semicircularis. The epithelium covers the choroid fissure, which otherwise would form a communication between the horn and the exterior. Through the choroid fissure the border of the velum interpositum projects toward the ventricle, and, push- ing the epithelium before it into the horn, forms the choroid plexus. Within the fissure there is a serrated free border of cortex called the dentate fascia^^ The dentate fascia folds medially in front of the hippocampal fissure and with the hippocampus major forms an S-shaped fold of the cortex. The S-shape is perfect in the left hemisphere, when viewed with the frontal lobes upward and the convex surface of the brain toward the spectator. The top of the letter is the fascia dentata; the superior curve is the hippocampus, produced by (39) Digitationes hippocampi. (40) Fascia dentata hippocampi. 42 THE BRAIN AND SPINAL CORD. the hippocampal fissure, the upper concavity; the lower con- cavity, open toward the ventricle, is the groove between the hippocampus major and the eminentia collateralis. THE THIRD VENTRICLE AND INTER-BRAIN. The inter-brain^i is medial in position. It is situated beneath the fornix and the layer of epithelium extending from the border of the fornix to the taenia semicircularis. The velum interpositum only intervenes between them. Laterally, it is bounded by the superior laminae of the in- ternal capsules. The ventricle of the inter-brain is the third^^ iri number. The third ventricle, therefore, is medi- ally located ; and is at a lower level than the ventricles of the hemispheres. Through the foramina of Monro, its anterior part (the aula) communicates with each lateral ventricle, and the aqueduct of Sylvius connects it, behind, with the fourth ventricle. The thir^d ventricle is fissure-like. It is a nar- row, vertical cleft about an inch in length from before back- ward and a quarter of an inch broad at its widest part. It separates the optic thalami, and extends almost to the infe- rior surface of the cerebrum. The roof follows the curve of the fornix and arches from the posterior commissure for- ward to the anterior commissure. The anterior wall extends from the upper border of the anterior commissure down to the optic recess, at the angle of flexion in the lamina cinerea. The -floor describes two arches, convex toward the ventricle. The first arch, very convex and short, stretches between the optic recess and the infundibulum, in which the floor reaches its lowest point. The distance from the infundibulum to the anterior orifice of the aqueduct of Sylvius is spanned by the (41) Diencephalon. (42) Ventriculus tertius. THE CEREBRUM. 43 second arch. It is long and rather flat. Its posterior ex- tremity is but a sixteenth of an inch below the posterior commissure; the anterior orifice of the Sylvian aqueduct separates them. The ventricle is thus contracted behind to the size of the Sylvian aqueduct, with which it is continuous. The lateral walls are close together throughout. At one point near the middle they come together and are joined by the gray, or middle, commissure.^^ Antero-superiorly, the lateral wall is perforated by the foramen of Monro.^* That foramen constitutes the slight separation between the front of the optic thalamus an!d the anterior pillar of the fornix. It opens into the lateral ventricle at the junction of the anterior horn with the body. The ependyma which lines the third ventricle is continuous through the foramen of Monro with the lining of the lateral ventricle. But one layer of the ependyma is present in the roof of the ventricle; that is the epithelial layer. The third ventricle, like all true ventricles, is occupied by cerebro^spinal fluid. The following are the boundaries of the third ventricle : Roof- Posterior commissure and commissura habenlarum, Eoof epithelium and pineal body. Velum interpositum and choroid plexuses, Fornix. Anterior wall — Epithelium, covering Pillars of fornix and anterior commissure. Lamina terminalis. Floor — Lamina cinerea and optic conunissure, (43) Massa intermedia. (44) Foramen interventriculare. 44 THE BRAIN AND SPINAL CORD. Tuber cinereum and infimdibuliun, Corpora albicantia, Posterior perforated lamina (of mid-brain). Tegmentum (of mid-brain). Posteriorly — Ventricle is continuous with aqueduct of Sylvius. Lateral walls — Optic thaJamus, Anterior pillar of the fornix, and Foramen of Monro between them. Roof. — ^A band of white fibers passes across the back part of the third ventricle and supports the posterior end of the roof epithelium. That band is the posterior com- missure.*^ It crosses immediately in front of the corpora quadrigemina. Beneath it is the anterior orifice of the aqueduct of Sylvius. The pineal body is above and behind it, and the commissure is inclosed between the ventral and dorsal pineal laminae. The posterior commissure stretches from one optic thalamus to the other; but most of its fibers terminate in the parieto-occipital region. It contains four sets of fibers, viz. : (1) Commissural fibers between the optic thalami ( ?) ; (2) the upper decussation of the posterior longitudinal bundles; (3) some fibers from the pineal stria, derived from the optic tract near the external geniculate body, which cross to the opposite nucleus (upper part) of the motor oculi (Darkschewitsch) ; and (4) fibers from the fillet crossing to the opposite hemisphere. The roof epithelium of the third ventricle stretches from the posterior commissure to the anterior commissure and laterally, is attached to the upper internal border of the optic thalamus. It is the supefrficial layer of the ependyma; (45) Commissura posterior. THE CEREBRUM. 45 but it is, here, the only adult representative of the roof of the neural tube (the thalamencephalon) . Anteriorly, this same epithelium investing the anterior commissure and pillars of the fornix, is the only representative of the neural wall (prosencephalon) down to the lamina terminalis. The roof epithelium presents two longitudinal folds suspenlded in the ventricle. The lower layer of the velum interpositum, con- stituting the superior choroid tela/'^ invests the roof epithe- lium of the third ventricle superiorly; and, dipping down into the longitudinal folds, that inferior layer of the velum interpositum forms the choroid plexuses'^^ of the third ventri- cle, which are continuous with those of the lateral ventricles through the foramina of Monro. At the back part in the middle line, there is a pouch-like evagination of the roof epithelium in the embyro, which develops into the pineal body. Pineal Body, or Conarium. — It is a cone-shaped body,^^ a quarter of an. inch high and one-sixth of an inch in diam- eter. Joined to the roof of the third ventricle by a flattened stalk or peduncle.^ *^ It is also called the epiphysis. The pineal body is situated in the floor of the great transverse fissure, directly below the splenium of the corpus callosum, and rests between the superior quadrigeminal bodies on the dorsal surface of the mid-brain. It is closely invested by pia mater. The pineal stalk splits into a dorsal and a ventral lamina. The ventral lamina, passing behind the posterior commissure, disappears beneath it; but the dorsal stretches forward over the commissure in continuity with the roof epithelium. The borders of the dorsal lamina are thick- (47) Tela choroidea ventriciili tertil. (48) Plexus choroideus ventrlculi tertii. (49) Corpus pineale. (50) Habenula. 46 THE BRAIN AND SPINAL CORD. ened, pineal strise,^^ and contain fibers which are derived from the anterior pillar of the fornix. (Note 1, add.,P. 225.) The pineal striae aJso contain optic fibers which pass through the posterior commissure to the nucleus of the oculomotor nerve. The interior of the pineal body is made up of closed fol- licles surrounded by ingrowths of connective tissue. The follicles are filled with epithelial cells mixed with calcareous matter, the brain-sand (acervulus cerebri). Calcareous de- posits are found also on the pineal stalk and along the choroid plexuses. The function of the pineal body is un- known. It is supposed to represent a cyclopian eye. In the Hatteria, a New Zealand lizard, it projects through the parietal foramen and presents an imperfect lens and retina and, in its long stalk, nerve fibers. The velum interpositum, a double triangular fold of pia mater, is interposed between the epithelium of the third ventricle and the medial part of the floor of the two lateral ventricles. Its apex is just behind the anterior commissure, and its base, directed backward, is continuous, by the upper layer, with the pia of the occipital lobes; and, by the inferior layer, it is continuous with the pia on the dorsal surface of the mid-brain anld cerebellum. Each border constitutes the choroid plexus of the lateral ventricle, and is seen (through the epithelium) in the floor of its body and along the inner wall of its descending horn. The inferior lamina of the velum interpositum forms the superior choroid tela;^^ medi- ally it invests the roof epithelium of the third ventricle, and, laterally, it covers the medial half of the upper surface of each optic thalamus. It forms the two choroid plexuses of (51) Stria medullaris thalami. (52) Tela choroidea ventriculi tertii. THE CEREBRUM. 47 the third ventricle,^^ which depend from its medial portion. Between the inferior and superior lamina is enclosed some arachnoid tissue; and the veins of Galen pass back through it from the foramina of Monro to the tentorium cerebelli, where they join with the inferior longitudinal sinus in form- ing the straight sinus. Anterior Wall. — The anterior commissures^ is a very dis- tinct round bundle of white fibers about an eighth of an inch in diameter. It is seen in the anterior wall of the third ventricle supporting the roof epithelium. The epithelium there bends down between the pillars of the fornix and in- vests the ventricular surface of the commissure. The an- terior commissure rests upon the upper extremity of the lamina terminalis, between the pillars of the fornix^, behind, an^ the rostrum of the corpus callosum, in front. With the last two structures it is developed from the hemisphere vesicles. It is the most important connecting link between the hemispheres in vertebrates withoxit a corpus callosum (all below mammals). Bending shortly backward the anterior commissure pierces the inferior part of the globus pallidus and then radiates toward the cortex, some of its fibers en- tering the external capsule. It contains two groups of fibers : (1) the anterior group/^ which is the commissure of the rhinencephalon, called the pars olfactoria; and (2) the pos- terior group,^^ the pars occipito-temporalis. The former connects the limbic iobes and joins each to the opposite olfac- tory tract; the latter ends in the inferior part of the occipital and in the temporal cortex. In man it is larger than the pars olfactoria. The upturned part of the lamina cinerea, called (53) Plexus choroideus ventriculi tertii. (54) Commissura anterior (cerebri). (55) Pars anterior. (56) Pars posterior. 48 THE BRAIN AND SPINAL CORD. lamina terminalis, extenlds from the anterior commissure and rostrum of the corpus callosum down to the flexure which incloses the optic recess ; it completes the anterior boundary of the third ventricle. The floor is very narrow. It is formed by the interpedun- cular structures plus the tegmentum, namely : lamina cinerea (with optic chiasma below it), tuber cinereum and infundib- ulum, corpora albicantia, posterior perforated lamina and the tegmentum. The last two are the middle and dorsal por- tions of the mid-brain; the others belong to the inter-brain, and all extend laterally beneath the optic thalami. The cor- pora albicantia, located on either side of the median line, may be excepted from the ventricular floor, as they are di- rectly beneath the thalami (see base of cerebrum). The third ventricle has its lateral wall formed by the optic thalamus and the anterior pillar of the fornix. The pillar of the fornix, diverging from its fellow, proceeds downward and backward to the corpus albicans through the medial part of the thalamus. In the ventricle it is covered by the ependy- mal epithelium. It bounds the foramen of Monro in front. Optic Thalamus. — It is the great ganglion of the inter- brain. The thalamus (tJialamos, a bed)^"^ is an important sensory way-station. In it or in the hypothalamic nuclei almost every impulse of general sensation, in its journey to the cerebral cortex, is transferred to a higher neurone. The third ventricle separates the thalami from each other, ex- cept at the mid-point where they are joined by the middle (gray) commissure.^s rp^g thalamus is situated behind and medial to the corpus striatum, and projects backward over the superior surface of the mid-brain. Laterally, it rests against the superior lamina of the internal capsule, which (57) Thalamus. (58) Massa intermedia. THE CEREBRUM. 49 separates it from the lenticular nucleus. The optic thal- amus is shaped like an egg, with the small end directed for- ward. It has an anterior and a posterior extremity and four surfaces: Superior, inferior, internal and external. Extremities. — The anterior extremity of the thalamus is lost in a large group of fibers (anterior stalk) which, run- ning through the anterior segment of the internal capsule, ends in the gyrus fornicatus and the frontal lobe of the cerebrum. The posterior end presents a large pillow-like prominence, the pulvinar; and beneath it is a smaller swelling, which forms the lowest point of the thalamus, the external geni- culate body. The internal geniculate body (of the mid- brain) is also continuous with this extremity internal to the pulvinar. The two geniculate bodies constitute the meta- thalamus. Surfaces. — The internal, or medial, surface of the optic thalamus forms the lateral wall of the third ventricle. It is joined to the internal surface of the opposite thalamus by the middle commissure. Both this and the superior surface are composed of a thin lamina of longitudinal white fibers, the stratum zonale. The superior surface of the thalamus is divided by an oblique groove, the choroid groove, corresponding in posi- tion to the border of the fornix, into two areas. The area inside the groove is covered by the velum interpositum and the fornix. Internall}^ it is bounded by the pineal stria and attachment of the roof epithelium. Posteriorly, next the stria, is a triangular depression bounded, behind, by a trans- verse groove in front of the corpora quadrigemina, and by a slight groove, the sulcus habenulae, externally. That de- 50 THE BRAIN AND SPINAL CORD. pressed surface is called the trigone of the habenula.^^ Be neath the triangle is one of the thalamic nuclei. The outer area is seen in the floor of the lateral ventricle. It presents an anterior elevation, the anterior tubercle/^ beneath which is the anterior nucleus of the thalamus. A sheet of epithe- lium, extending from the fornix to the taenia semicircularis, covers this outer area and separates it from the ventricular cavity. A special lamina of fibers, the external medullary lamina, derived from the fillet, forms the external surface of the optic thalamus and rests upon the superior lamina of the internal capsule. The inferior surface blends with the superior surface of the tegmentum and substantia nigra, and forms the laminae and nuclei of the tegmental region. (See below.) Hypothalamic tegmental regional is composeid of three layers: (1) Stratum dorsale next the optic thalamus; (2) Zona incerta, the middle; and (3) the nucleus of Luys, or hypothalamic body, the inferior. The nucleus of Luys^^ is but the terminal part of the substantia nigra. The reticu- lar formation of the tegmentum, continuing beneath the optic thalamus, forms the zona incerta. The stratum dorsale is made up as follows: (a) Fibers from the posterior longi- tudinal bundle (Meynert) ; (b) the superior peduncle of cerebellum (Forel), in which is the upper end of the red nucleus^^ of the tegmentum; and (c) the fillet.^* The external geniculate body (geniculum, a little knot or (59) Trig-onum habenulse. (60) Tuberculum anterius thalaml. (61) Hypothalamus. (62) Nucleus hypothalamicus. (63) Nucleus ruber. (64) Lemniscus. THE CEREBRUM. 51 knee)^'^'^ forms a slight swelling at the lowest point of the optic thalamus. It marks the apparent end of the outer root of the optic tract and is the terminal nucleus of eighty per cent.of its fibers. It is joined to the superior quadrigeminal body -by the superior brachium. In appearance it is dark col- ored and laminated; its gray matter, which contains pig- mented multipolar cell-bodies, is divided into thick layers by thin laminae of fibers from the optic tract. The processes of the multipolar cell-bodies help to form the optic radiations. The internal geniculate body^<^ belongs to the mid-brain. It is placed at the end of the inner root, as the external genic- ulate is at the end of the outer root, of the optic tract. It rises up from the groove between the optic thalamus and corpora quadrigemina, and is joineid to the inferior quadri- geminal body by the inferior brachium. The superior bra- chium sweeps around it in front, passing between it and the external geniculate body. The internal geniculate body is gray iii color and is not laminated. Its cell-bodies are small, and fusiform in shape. They perhaps give origin to the in- tercerebral fibers (Gudden) of the optic tract and to a large number of the acustic radiations. (65) Corpus geniculatum laterale. (66) Corpus geniculatum mediale. CHAPTER III. MID-BRAIN. The brain just behind the cerebrum is the mid-brain.^ It is the connecting link between the inter-brain and the hemi- spheres, in front, and the pons, behind. This has suggested the name isthmus, sometimes applied to it, though isthmus is more specifically applied to the constriction behind the cor- pora quadrigemina. It is developed from the middle of the five brain vesicles, the mesencephalon. The cerebral hemi- spheres almost conceal it from view; they overhang it dor- sally, and the temporal lobes, inclosing it between them, bend medially and cover part of its ventral surface. Only the median part of the ventral surface is visible in the complete brain. The form of the mid-brain resembles a flattened cylinder. Its axis, a half inch long, is pointed upward and forward, and its long diameter, which varies from an inch to an inch and a quarter in length, is directed transversely. SURFACES. The mid-brain has four surfaces, viz., the ventral and dorsal, which are free, and the superior and inferior, repre- senting the ends of the cylinder, which are attached. The two latter are parallel with each other and are formed by section. The superior surface, sloping downward and forward, meets the ventral surface at an acute angle. Its inclination is that of the back part of the floor of the third ventricle. (1) Isthmus rhombencephali and mesencephalon. MID-BRAIN. 53 External to the floor of the ventricle, it is attached to the optic thalami anid internal capsules. The blending of it with the thalami forms the structures of the hypothalamic teg- mental regions, and the continuations of the extreme lateral portions, the crustse, constitute the superior laminae of the internal capsules of the hemispheres. In the median line be- hind the third ventricle it is attached to the posterior com- n^issure. The inferior surface joins the upper surface of the pons. It is a little narrower than the superior surface. It is about one inch broad and measures three-quarters of an inch dor so- ventrally. The ventral surface of the mid-brain looks downward and forward. It is deeply grooved longitudinally by the median stdcus,^ and is slightly concave from above downward. It is separated on either side from the dorsal surface by the sulcus lateralis.^ Though partially concealed by the tem- poral lobes of the cerebrum, the ventral surface is unattached. It is formed by a prominent band, the crusta,'^ at either side; and by a median structure, the posterior perforated lamina,^ which is inclosed between the two crustae. The posterior per- forated lamina forms the floor of the median sulcus. The inner border of the crusta is free and overhangs the per- forated lamina slightly. Thus is formed the oculomotor groove^ between the crusta and perforated lamina, whence the third cranial nerve takes its superficial origin. The fourth nerve courses forward over the ventral surface, but is not attached to it. (2) Fossa interpeduncularis. (3) Sulcus lateralis mesencephali. (4) Basis pedunculi. (5) Substantia perforata posterior. (6) Sulcus nervi oculomotoril. 54 THE BRAIN AND SPINAL CORD. The dorsal surface of the mid-brain, though free, is en- tirely concealed by the cerebral hemispheres. It forms part of the floor of the great transverse fissure and is covered by pia mater. The lateral sulcus bounds it on each side. From the sulcus lateralis it elevates abruptly toward the median line, where it presents a longitudinal groove. This produces two ridges which are subdivided by a transver-se groove into the four eminences (colliculi) of the corpora quadngemina. On either side, anterior and a little external to the quadri- geminal bodies, is the internal geniculate body. There are thus presented six eminences on the dorsal surface of the mid-brain. The entire dorsal surface is formed by the teg- mentum. INTERIOR. The mid-brain is made up of three great divisions, namely : (1) The ventral part, composed of the two crustae; (2) the substantia nigra, which is the middle part; and (3) the dorsal part, called the tegmentum, composed of lateral halves united by a raphe. The crustae'^ are two rounded bands of white fibers, limited by the medial and the lateral sulci, which form the ventral part of the mid-brain. They are in contact at the front of the pons, from which they diverge upward and forward and pierce the inferior surface of the cerebrum beneath the optic tracts. Entering the cerebrum just external to the optic thal- amus, the fibers of each crusta spread out, fan-like, in the internal capsule. Excepting the medial fillet, a part of which enters the inferior lamina, and a part of the temporal cerebro- corticopontal tract which takes the same course, the crusta enters only into the superior lamina of that inner capsule. (7) Basis pedunculi (sing-.). MID-BRAIN. 55 The deep portion of each crusta is occupied by the interme- diate bundle, whose fibers arise in the corpus striatum and terminate in the nucleus pontis (Flechsig). The superficial portion should be studied in three parts: (1) The outer fifth of each crusta, the temporal cerebro- corticopontal tract, is composed of efferent fibers which rise in the temporal cortex, in the superior, middle and inferior gyri (Dejerine). Proceeding through the inferior lamina and the occipital segment of the superior lamina of the inter- nal capsule, and through the lateral part of the crusta, they terminate chiefly in the nucleus of the pons; a few end in motor nuclei of cranial nerves (Spitzka). The fibers are probably interrupted in the thalamus or lenticular nucleus. They form a segment of the indirect motor path. These fibers are meduUated later than the pyramidal tract (Flech- sig). (2) The middle three-fifths ot the crusta is for the most part motor. It is called the pyramidal tract.^ Its fibers rise in the Eolandic area of the cerebral cortex; they form the genu and anterior two-thirds of the posterior segment of the internal capsule, the middle three-fifths of the crusta, the ventral longitudinal fibers of the pons, and the pyramid of the medulla. Below the medulla they are continued in the direct and crossed pyramidal tracts of the spinal cord. Those fibers of the pyramidal tract which innervate the muscles of speech and of the face run through the genu of the internal capsule and constitute the medial portion of the tract. Im- mediately behind the face fibers, in the capsula interna, and external to them, in the tract, are fibers which innervate the muscles of the arm. Still behind these, in the internal cap- sule, and external to them, in the pyramidal tract of the (8) Fasciculus longitudinalis pyramidalis. 56 THE BRAIN AND SPINAL CORD. crusta, are fibers for the innervation of the trunk and leg mnscleSj the leg fibers being most posterior and most external. Intermingled with the pyramidal fibers are a few fibers from the cerebellum. The cerebellar fibers, upon reaching the pons through the middle peduncle of the cerebellum, ascend with tlie ventral longitudinal fibers of the pons and are sparsely scattered throughout the crusta. (3) The inne7' fifth of the crusta is composed of the me- dial fillet and the frontal cerebro-corticopontal tract. The origin of the latter is probably in the pre-Eolandic cortex, at the anterior end of the first frontal and at the feet of the second and third frontal gyri ; and, perhaps, in the middle of the gyrus fornicatus. It is motor. This motor tract is con- tained in the anterior segment of the upper lamina of the in- ternal capsule. Its termination is in the nucleus of the pons and in the motor nuclei of cranial nerves (Flechsig). It con- stitutes a stage of an indirect motor path, like the fibers of the outer fifth of the crusta, and the indirect path is con- tinued to the opposite half of the cerebellum by neurones whose cell-bodies are in the nucleus pontis (Flechsig). The medial fillet^ (sensory) exists as a distinct bundle in this part of the crusta. Superiorly, it enters the hypothalamic region, and ends in the ventre- lateral nucleus of the optic thalamus. A few of its fibers join the ansae lenticularis et peduncularis and run uninterrupted to the cortex ; they form a part of the inferior lamina of the internal capsule, and then, of the medullary laminae of the lenticular nucleus. The medial fil- let is the afferent cerebral tract of the spinal and of all the cranial nerves with the exception of the cochlear division of the auditory. The Substantia Nigra. — The central part of the mid-brain (9) Lemniscus medialis. MID-BRAIN. 57 is a sheet of pigmented gray matter. The substantia nigra is visible at the base of the brain between the crustse, where it is called the posterior perforated lamina,^^ and its margin comes to the surface in each lateral sulcus. Antero-pos- teriorly, it extends from the pons forward to the corpora albican tia and nucleus of Luys. Doisal to it is the teg- mentum. Transversely, the substantia nigra is convex down- ward, but it is slightly concave longitudinally. The third nerve pierces it and comes out through the oculomotor groove. It contains small pigmented multipolar cell-bodies, some of which constitute a relay for certain fibers of the medial fillet (Barker). There is an aggregation of these cells located medially just in front of the pons, the inter- peduncular ganglion}'^ According to Forel, this ganglion is connected by a bundle of fibers, the fasciculus retroflexus, with the nucleus habenulae of the optic thalamus. The an- tero-lateral portion of the substantia nigra forms the nucleus of Luys, or nucleus hypotlialamicus, on either side. The nucleus Luysi lies ventro-lateral to the red nucleus,^ ^ ^nd is separated from it by the zona incerta. The Tegmentum. — The dorsal division of the mid-brain, being the largest and covering the other two divisions, is in consequence called the tegmentum (the cover). It fits ventrally into the concavity of the substantia nigra, and is bounded by the lateral sulcus on each side. Dorsally, it pre- sents the internal geniculate bodies and the corpora quadri- gemina. The tegmentum is very thick medially. In trans- verse section it has a pentagonal form, the curve of the sub- stantia nigra representing two sides. Superiorly, the an- terior extremity of the tegmentum blends with the optic (10) Substantia perforata posterior. (U) Ganglion interpedunculare. (12) Nucleus ruber. 58 THE BRAIN AND SPINAL CORD. thalami in the hypothalamic regions. The tegmentum is continuous with the pons behind (caudalward). It contains the cavity of the mid-brain, the aqueductus Sylvii.^^ The Aqueduct of Sylvius. — ^The aqueduct is a very slender canal connecting the third and fourth ventricles. So it is the "iter a tertia ad quartum ventriculum." It is situated near the dorsal surface of the tegmentum, directly beneath the sulcus longitudinalis. It is a half-inch long. In shape it is V-like, above; elliptical, in the middle, with a vertical major axis; and T-form, below, where it joins the fourth ventricle. Its height varies between a sixteenth and an eighth of an inch. Like other ventricles, it is lined with ependyma. A layer of gray matter, thickest on the sides and floor, sur- rounds the aqueduct of Sylvius. It is continuous with the gray matter of the fourth ventricle. In it are the nuclei of the oculomotor (third) and the trochlear (fourth) cranial nerves. Nuclei of the Oculomotor and Trochlear Nerves. — Both nuclei extend the entire length of the aqueduct, and the oculomotor^* is prolonged into the wall of the third ventricle, where it receives a bundle of fibers from the opposite pineal stria and optic tract. The nuclei are composed of several elongated masses of gray matter, which contain cell-bodies of various sizes. They lie. side by side in each half of the floor of the aqueduct, and are associated with the optic tract (external root) by fibers in the posterior commissure and by association neurones in the superior quadrigeminal bodies. By this connection certain reflex ocular movement, accommo- dation for distance and pupillary contraction are accom- plished. The oculomotor nucleus is next the median line and behind unites with its fellow across it. For the most part (13) Aqueductus cerebri. (14) Nucleus oculomotorius. MID-BRAIN. 59 the third nerve, motor oculi, rises from the nucleus of the same side; but it also contains crossed fibers from the oppo- site nucleus and from the posterior longitudinal bundle of the opposite side. Some of the last are derived from the nucleus of the abducent (sixth) nerve and, after crossing to the third nerve, supply the internal rectus of one eyeball; while the sixth, rising from the same nucleus, supplies the external rectus of the other eye. Thus is conjugate deviation accounted for. The third nerve passes down to the oculo- motor groove through tegmentum and substantia nigra. The root fibers of the fourth nerve, trochlear (patheticus)^^ pro- ceed dorsally and caudalward from the nucleus. They de- cussate with the fibers from the opposite nucleus in the su- perior medullary velum (the valve of Yieussens), from which they emerge on either side of the frenulum. They then con- tinue in the opposite nerve around the side and over the ventral surface of the mid-brain. The nucleus of the troch- lear nerve (also the abducent) likewise receives impulses from the optic tract. The corpora quadrigemina are four bodies (colliculi) which stand upon the quadrigeminal lamina and constitute a large part of the dorsal surface of the mid-brain. They are seen in the floor of the great transverse fissure, invested by pia mater and overhung, anteriorly, by the pineal body. The crucial groove separates them and marks out a larger su- perior pair,^^ elongated from before backward, and a hemi- spherical inferior pair.^"^ The internal geniculate body lies in front and a little external to the corpora quadrigemina. A ridge made up of white fibers, the superior brachium,^^ joins (15) N. trochlearis. (16) Colliculi superiores. (17) Colliculi inferiores. (18) Brachium quadrlgeminum superius. 60 THE BRAIN AND SPINAL CORD. each superior quadrigeminal body to the corresponding exter- nal geniculate body, sweeping around the internal geniculate body in front and externally. The inferior brachium^^ forms an oblique ridge between the inferior quadrigeminal body and the corpus geniculatum internum of the same side. The su- perior peduncle of the cerebellum and lateral fiUet^o form two ridges which end at the back of each inferior quadri- geminal body. The corpora quadrigeniina (superior colli- culi) constitute the great center for the association of ocular movements and reflexes with optic and auditory impulses and impulses of common sensation. The inferior colliculi con- stitute a relay, or way-station, in the auditory path. Structure. — The corpora are composed chiefly of gray mat- ter. The upper and lower fillet and the valve of Vieussens form a layer of fibers, the quadrigeminal lamina, upon which they rest and which separates them from the gray matter around the aqueduct of Sylvius. They also contain many fibers in their interior and are covered, superficially, by a thin layer of white matter. ( See quadrigeminal bodies, Chapter IV., pages 82-83.) The internal geniculate bodies^i form a part of the teg- mentum. They are derived from the mesencephalon with the remainder of the mid-brain to which they belong ; but for convenience, they were considered with the external genicu- late bodies under the heading "inter-brain," which see. The internal geniculate bodies form the relay in the auditory path next above the inferior quadrigeminal bodies. Fibers of the Tegmentum. — The tegmentum is a continua- tion of the dorsal longitudinal fibers and the formatio reticu- (19) B. quadrigeminum inferius. (20) Lemniscus lateralis. (21) Corpus geniculatum mediale (sing.). MID-BRAIN. OX laris of the pons, and of the gray matter in the floor of the fourth ventricle; and, in addition, has the geniculate and quadrigeminal ganglia forming its dorsal portion. It is composed of symmetrical halves united by a median raphe. Each half contains innumerable transverse and longitudinal fibers with small masses of gray matter in the meshes. In- tersecting the many transverse fibers are six distinct bundles of longitudinal fibers. They descend from cerebrum and mid-brain, or ascend from parts below. Those six bundles are as follows: (1) The Posterior Longitudinal Bundle^^ lies beside the raphe, just ventral to the gray matter of the Sylvian aque- duct. It is traceable from the anterior cornu of gray mat- ter in the spinal cord where its ascending fibers rise (Tscher- mak). Being chiefly an association tract, it receives fibers, in the pons, from the cerebellum; and from sensory nuclei of the cranial nerves, in the medulla and pons. It carries motor fibers from the sixth to the third nerve; also descend- ing motor fibers from the nucleus of the motor oculi to the genu of the seventh, or facial, nerve. These latter supply the frontalis, pyramidalis nasi, orbicularis palpebrarum and cor- rugator supercilii muscles. Through the raphe the posterior longitudinal bundle partially decussates with its fellow (lower decussation). These fibers pass into the opposite third and fourth and other motor cranial nuclei. The re- mainder of the bundle, decussating through the posterior commissure (upper decussation), ends in the pineal body and stratum dorsale of the hypothalamic region. It connects the cerebellum with opposite nuclei of the cranial nerves and the latter with each other. It associates the motor oculi with (22) Fasciculus longitudinalis medialis. 62 THE BRAIN AND SPINAL CORD. the abducent and facial nerves, and the optic with the ab- ducent. It also associates spinal and cranial nerves. (2) Anterior Longitudinal Bundle. — Just ventral to the posterior longitudinal bundle is the fasciculus from the su- perior corpus quadrigeminum to the cilio-spinal and other centers in the cord. It is the pupillo-dilator tract. (3) The Fillet. — Near the upper end of the pons, in the ventral part of the formatio reticularis, the fillet, or lemnis- cus, forms a very broad band of fibers on either side of the median raphe. The fillet is equal in width to half the trans- verse diameter of the mid-brain. It continues into the ven- tral portion of the tegmentum, but immediately divides into two fasciculi, viz., the interolivary fillet,^^ and the lateral, or lower, fillet.^^ Farther forward a small bundle leaves the lateral part of the interolivar}^ fillet and runs up to the su- perior quadrigeminal body. That bundle is called the su- perior fillet,25 and what remains is the medial fillet.^^ Function. — The fillet forms a segment in the direct sen- sory tract. It carries spinal and cranial impulses to the cor- pora quadrigemina and optic thalamus. Interolivary Fillet. — The fibers composing the interolivary fillet rise chiefly in the nucleus gracilis and nucleus cuneatus of the opposite side of the medulla oblongata. They cross over in the sensory decussation of the medulla ; and, excepting a small bundle, terminate in the ventro-lateral nucleus of the optic thalamus. Fibers are added from masses of gray mat- ter along the whole course of the interolivary fillet, especially from the terminal nuclei of sensory cranial nerves; and (23) Lemniscus interolivaris (comprising L. medialis and L. supe- rior). (24) Lemniscus lateralis. (25) Lemniscus superior. (26) Lemniscus medialis. MID-BRAIN. 63 others, also, from the cerebellum. On the other hand, cer- tain fibers leave the fillet and end in the nuclei along its course, that is, are interrupted, and other fibers continue in their stead. A small bundle of fibers separating from the lateral part of the interolivary fillet and running to the su- perior quadrigeminal body, forms the superior fillet. It as- sociates ocular movements with sensations from cranial and spinal nerves. The medial fillet bends ventrally as it runs through the mid-brain. It pierces the substantia nigra, in which it undergoes a partial relay, and then continues for- ward, with the inner fifth of the crusta, to its termination in the thalamus. From the thalamus the impulses are carried by the anterior stalk and ansae lenticularis et peduncularis to the soma esthetic area of the cortex. The lateral, or lower, fillet^'^ forms an oblique ridge on the dorsum of the tegmentum. It trends upward and in- ward over the superior cerebellar peduncle to the inferior quadrigeminal body, where its fibers terminate. It rises chiefly from the ventral and dorsal parts of the cochlear nuclei (principally the opposite one) and ends in the inferior quad- rigeminal body. It undergoes partial relay in the nucleus of the superior olive and of the trapezoid body on each side, and the nucleus of the lateral fillet on the same side, and it receives a small bundle of fibers from the anterolateral as- cending, cerebellar tract. The greater number of its fibers cross through the trapezium; some are uncrossed. Thus the lateral fillet forms the second stage in the auditory conduc- tion path. Tlie auditory nerve constitutes the first stage, the lateral fillet the second stage,, the inferior brachium the third, and the acustic radiations the fourth stage. The last (27) Lemniscus lateralis. 64 THE BRAIN AND SPINAL CORD. stage ends in the cortex of the superior and the transverse temporal convolutions. (4) The Superior Pedunde^^ of the cerebellum continues upward from the dorsal surface of the pons. It forms a ridge near the median line of the mid-brain which ends in front at the inferior corpus quadrigeminum. The lower fillet winds inward over its anterior extremity. It is joined to its fellow by a sheet of white matter, the valve of Vieussens.^^ The fibers of the cerebellar peduncles bend ventrally beneath the corpora quadrigemina and then, for the most part, decussate, inferior to the iter, through the median raphe. These crossed fibers with the few uncrossed run forward toward the in- ferior surface of the optic thalamus, where they inclose the red nucleus, and help to form the stratum dorsale of the hy- pothalamic region (Forel). Many of the fibers terminate in the red nucleus and from it others rise and proceed forward to the thalamus. Though most of the superior cerebellar pe- duncle is centripetal and forms a segment of an indirect sen- sory tract, it also contains effereiit fibers which rise in the red nucleus. (5) The Olivary Fasciculus. — This is the bundle^^ which takes form at the inferior olive, where it probably rises. It runs through the formatio reticularis of medulla and pons up to the mid-brain. In the tegmentum it pierces the de- cussation of the superior cerebellar peduncles, running ven- tral to the longitudinal bundles; and then, bending lateral- ward, it ascends external to the posterior longitudinal bundle. It ends in the globus pallidus of the lenticular nucleus (Flechsig). Flechsig believes that the olivary bundle and (28) Brachium conjunctivum. (29) Velum modulare anterius. (30) Fasciculus tegmenti centralis. MID-BRAIN. 65 the fasciculus triangularis of Helwig (in the spinal cord) are parts of the same afferent conduction path. (6) The Crossed Descending Tract of the Red Nucleus. — Formed by axones from that nucleus, it immediately de- cussates with its fellow of the opposite side and descends, in the medial part of the lateral fillet, to the medulla; it then mingles with the antero-lateral ascending cerebellar tract, in the medulla; and, in the cord, occupies the dorso-lateral part of the crossed pyramidal tract. It ends in the lateral horn and center of the gray crescent. It may be traced to the lumbar segments of the spinal cord. CHAPTER IV. THE GRAY AND WHITE MATTER OF THE CERE- BRUM AND MID-BRAIN. In the mid-brain, white matter is found in the crustae and tegmentum, separated by the gray substantia nigra; and on its dorsum are the corpora quadrigemina and internal geniculate bodies composed of gray matter. Gray matter forms nearly the whole of the inter-brain. The deep part of the hemispheres is white matter; a thin envelope of gray matter, the cortex, incloses it. Imbedded in that white mat- ter, is* the basal ganglion of the hemisphere, called the corpus striatum. Both the gray and the white matter are richly supplied with blood vessels. The Neurone. — The essential element in the nervous sys- tem is the neurone. The neurone comprises the cell-body, its processes and end-organs. The cell-body, perikaryon, or nevr rone center, is a reticulated mass of protoplasm of variable form, and ranges between ten microns and fifty microns in size. It is nucleated and may possess several nucleoli. Its shape, which is spherical, fusiform, pyramidal, stellate or polygonal, is dependent upon the number and mode of or- igin of its processes. The processes of the neurone are from one to eight or a dozen in number and are of two kinds, namely, the dendrites and the axones. Dendrites, like the cell-body, are protoplasmic in composition and of irregular contour, except in sensory nerves, where they are fibrillar, like axones. They branch richly and end in beaded points. THE GRAY AND WHITE MATTER. 6/ They conduct toward the cell-body and are therefore affer- ent, or sensory. (N. 2, Add.) Axones, or neuraxones, are smooth and fibrillar in character. They give off many side branches, called collaterals, and terminate by multiple di- vision in an end-hrush, which is in relation with another neurone or with a muscle fiber. In the latter case the fibers of the end-brush spread out into disc-like platelets, motorial end-plates, and underneath the sarcolemmse apply themselves to the fibers of a muscle. Axones conduct from the neurone center. They are efferent, or motor. Both axones and den- drites are usually insulated by the white substance of Schwann, which forms their medullary sheaths. In all prob- ability neurones differ in chemical constitution and in elec- tric status, hence chemicals, electricity and diseases appear to exercise a selective power and affect certain neurones with- out influencing others (see note on neurone, p. 68). In the brain and spinal cord and in the optic nerves two forms of sustentacular tissue are found supporting the neu- rones. (1) Neuroglia, which is most abundant in gray mat- ter. It is an epiblastic structure made up of richly branched nucleated cells whose processes form a fine reticulation in the larger meshes of the connective tissue network (N. 3, Add.) (2) Connective tissue network. — That is of mesoblaa- tic origin and is formed by branching processes from the in- ner surface of the pia mater. It transmits the blood-vessels into the nervous substance. The neurones constitute 53 per cent of the brain and cord (cell-bodies, 6 per cent) and the sustentacular tissue 47 per cent (Donaldson). The white matter of the cerebro-spinal axis is made up chiefly of bundles of meduUated axones imbedded in neuroglia and supported by connective tissue. The fibers possess no neurolemma. 68 THE BRAIN AND SPINAL CORD. The gray matter of the central nervous system is composed of cell-bodies and dendrites, chiefly, but also contains axones. These nerve elements are supported by connective tissue and blood vessels and are imbedded in a great abundance of neu- roglia. The nerve fibers in the gray matter are to a large extent non-meduUated. NOTE. In the first edition of this work the name of the nerve ele- ment was spelled "neuron" according to Waldeyer. But the new spelling, already used by Profs. Barker and Gordinier in their excellent works, has been employed in the revised edition to avoid confusion. Shaefer uses neuron in the sense of axone and Wilder of Cornell makes it synonymous with cerebro-spinal axis. The neurone is a nervous entity and in the embryo is struc- turally independent of all other neurones. When fully de- veloped in man perhaps a very small number of neurones are united together by concrescence or protoplasmic bridges, but their predominant relation is certainly that of contact, or synapsis. TYPES OF NEURONES. 1. The first type has a long axone, which preserves its identity though it may give oS many collaterals. Found in brain and spinal cord (Deiter). 2. The second type has a short axone, breaking at once into branches of apparently equal importance, the dendrax- one. Found in cerebrum and cerebellum (Golgi^s cells). 3. The third type has two or more axones — diaxone, tri- axone, polyaxone — as in the first layer of the cerebral cortex (Cajal). THE GRAY AND WHITE MATTER. 69 ORDERS OF NEURONES. 1. The first order has distal process in relation with the periphery, as spinal-ganglion or anterior comu neurones. 2. The second order has cell-hody or distal process in re- lation with neurone of first order. In like manner there are neurones of the third, fourth, fifth order, etc. FUNCTIONS OF NEURONES. 1. Afferent. 2. Associative. 3. Efferent. QUALITIES PECULIAR TO DENDRITES : 1. They may be absent or very numerous. 2. They are protoplasmic in composition like the cell-body. 3. In contour they are irregular, knobbed or gemmulated. Except in sensory cranial and spinal nerves (Cajal). 4. End in sharp points, or in sensory neurones of first or- der, they may end within bulbous or spherical end- organs. 5. Afferent in conduction: (1) sensory; (2) excito-re- flex; and (3) trophic (?). QUALITIES PECULIAR TO AXONES I 1. Single or multiple (absent in latent neurones). 2. Fibrillar in character. 3. Smooth and regular in contour. 4. Terminate in form of end-tufts which in motor neurones of the first order form motorial end-plates. 5. Efferent in conduction: (1) motor; (2) inhibitory; (3) trophic ( ?) ; and (4) secretory ( ?). On section both dendrite and axone undergo Wallerian degeneration in the disconnected part. That part remaining in connection with the cell-body atrophies and degenerates late, degeneration of Nissl. yO THE BRAIN AND SPINAL CORD. The gray matter of the cerebrum and mid-brain is con- veniently grouped into three classes: I. Cortical. II. Ganglionar. III. Central, or Ventricular. I. The Cortical Gray Matter. It consists of a thin envelope, the cortex (or bark), which forms the surface of the hemispheres and incloses the (white) medulla, the centrum semiovale. The cortex varies in thick- ness from a line to a* quarter of an inch. Thickest on the surface of the convolution, it grows thinner to the bottom of the sulci. It is of a reddish, or yellowish, gray color depend- ing on the richness of the blood supply. By long observation of lesions in the brain and by anatomical and physiological investigation the cortex has been mapped out into quite defi- nite areas. Psychic function, probably, is dependent upon the associated activity of all parts of the brain; but common sensory and motor regions have been defined with considera- ble exactness. The latter are found in the equatorial zone of the hemisphere (Figure 1). That sensori-motor region is called the motor area (or Ealandic area) when referring to the efferent, or motor, tracts which rise in it; and, when ref- erence is made to the sensory tracts which terminate in it, the sensori-motor region is called the somcesthetic area. Notice in Fig. 1 that the motor speech center and head area comprise the foot of the inferior frontal convolution and the lower two- fourths of the central gyri; the writing center of Gordinier and the upper extremity area occupy the foot of the middle frontal, a part of the superior frontal and the third fourth (numbered upward) of the central convolutions; and the trunh and lower extremity areas are contained in the upper THE GRAY AND WHITE MATTER. 7 1 one-fourth of the central convolutions and in the superior pa- rietal gyrus. The head, shoulder, trunk and lower extremity are also represented, and in this order, in the marginal gyrus, the paracentral and quadrate lobules (see Fig. 2). In the same figure the centers of smell and taste may be observed in the uncus and hippocampal convolution and the visual cen- ter in the cuneus. The latter extends somewhat into the con- vex portion of the occipital lobe. Locate the remaining spe- cial centers on the convex surface (see Fig. 1). In the angu- lar and occipital convolutions is the center for visual mem- ories; in the supramarginal gyrus appears to be the center for motor memories; the sensory auditory center is seen in third and fourth fifths of the superior and in the transverse temporal gyri, and the center of auditory memories is in the immediately adjacent cortex. The naming center is probably in the third temporal convolution. All the above motor, somgesthetic and special sense areas are provided with projection fibers which connect them with definite muscle groups and surface regions and with the organs of special sense. Other parts of the cerebral cor- tex possess no projection fibers; they are believed to be asso- ciative in function. Anterior association center. — According to Flechsig, that part of the frontal cortex which is anterior to the motor and somaesthetic regions determines the temper- ament and individuality of the person ; while the posterior as- sociation center, composed of those portions of cortex situated between the sensory and motor regions of the equatorial zone, in front, and the visual cortex of the occipital lobe, behind, determine the intelleetuality of the individual. To acquire knowledge of the external world is thus the function of the posterior association center. Flechsig regards the island of 72 THE BRAIN AND SPINAL CORD. Eeil as the middle association center and lesions in it have been found associated wfth paraphasia. Destructive lesions of parts of the motor or sensory cortex cause merely loss of certain motions and sensations repre- sented by those parts, but ablation of association centers dis- connects the sensory, the memory and the motor regions (as in aphasia), causes change of temperament and impairment of the so-called moral and intellectual faculties. Ablation of the visual memory center or auditory memory center pro- duces mind-blindness in the former and in the latter mind- deafness. To the naked eye a fresh section of the cerebral cortex shows a stratified arrangement; sometimes three gray lam- inae can be made out which are separated by the inner and outer white lines of Bailarger; and, in the hippocampus ma- jor, a superficial (reticulated) white layer also is easily seen. A typical section of cortex, which is usually taken from the parietal lobe, presents under the microscope five layers, as follows : (1) The Superficial, Molecular, or Neurogliar Layer.- — It is next the pia mater and is believed to be associative in function. Neuroglia forms the bulk of it, but it contains (a) a few irregular cell-bodies (Neurones of Cajal) possess- ing dendritic and from one to three axonic processes; and (b) a fine network composed of gray and medullated nerve fibers. These medullated fibers form the superficial white layer, above referred to, visible to the naked eye in the hip- pocampus major. The fibers in the neurogliar layer are for the most part dendrites of cell-bodies in adjacent laminae. The neurones of the first layer probably give rise to the short association fibers of the cerebral cortex. (N. 4, Add.) (2) The Second Layer is the layer of small pyramids. THE GRAY AND WHITE MATTER. 73 The pyramids are closely packed together. They point to- ward the pia. Their dendrites run outward and ramify in the neurogliar layer; their bases, from which the axones issue, are directed toward the white core of the convolution. The axones, after piercing the deeper gray laminae, receive the white substance of Schwann and enter into the forma- tion of the medulla (the centrum semiovale) of the hemi- sphere. The small pyramids are believed to be chiefly com- missural and associative in function. (3) Third, the Layer of Large Pyramids. — The large pyramids have the same direction as the small ones. They are arranged in elongated groups separated by radiating fibers. The pyramids are largest in the Eolandic area, and the grouping is most distinct near the underlying fourth layer. The function of the large pyramids is chiefly motor (Dana), but it is also commissural and associative (Cajal). Their dendritic processes pass outward; their axones, as me- duUated fibers, run down into the white center and capsula interna. Seven or eight collaterals are given off from each axis-cylinder process before it becomes meduUated, and these collaterals ramify in the adjacent gray matter, basal ganglia, etc. The third layer is as thick as the two overlying it; it varies between one-fiftieth and one-twenty-fifth of an inch. Its formation is like that of the cornu Ammonis, the hippo- campus major. (4) Fourth, the poiyviorphons layer, is a very thin one, about a hundredth of an inch in thickness. Its cell-bodies are small and irregular. They possess many dendrites and one axone, or axis-cylinder process. A few of the latter, pierc- ing the third and second layers of gray substance, ramify in the first; the larger number of them proceed into the white 74 THE BRAIN AND SPINAL CORD. center and comprise a great number of the commissural and long association fibers (Cajal). Probably others become ef- ferent projection fibers. (Note 5, Add.) (5) Fifth. — This is the layer of fusiform cell-bodies. It has the formation of the claustrum, hence the synonym for the fifth layer, the claustral formation. It is placed next the white center. It is a thick layer, one-twenty-fifth of an inch, and merges imperceptibly into the medulla beneath it. The cell-bodies in the main have their long axes perpen- dicular to the surface of the hemisphere; but, beneath the fissures, they are parallel with it. In the convolutions they lie between the radiating fibers. Under the sulci they are parallel with the association fibers which join adjacent gyri. The commissural and long association fibers belong for the most part to the fusiform and polymorphous neurones. (N. 5 and 6, Add.) To this typical cortex there are four principal exceptions, viz. : (a) On the medial surface of the occipital lobe, near the cdlcarine fissure, there are six to eight layers produced by the division of the layer of large pyramids by a lamina of irregular cell-bodies, with or without the presence of the normal fourth layer. The latter may divide the fifth layer. There are very few large pyramids in this situation. (b) The gray cap of the olfactory hulh has but four layers, namely: first, the nerve fiber layer composed of the non-medullated fibers of the olfactory nerves which join the bulb from below; second, the stratum glomerulosum, the glomeruli being made up of the synapses formed by the ol- factory fibers and the dendrites of the mitral neurones; third, the layer of mitral cell-bodies, whose protoplasmic pro- cesses ramify in the second layer and whose axones pass into THE GRAY AND WHITE MATTER. 75 the medullary stem, after piercing the granular layer; and, fourth, the granular layer, which lies next the medullary stem and is composed of small irregular neurone-centers, like those in the rust-colored granular layer of the cerebellum. The last two (the third and fourth) are sometimes called the granular layer, thus reducing the number to three. The axis-cylinder processes of the mitral (or conical) neurones, medullated, form the olfactory tract. Destruction of the olfactory bulb, olfactory tract or olfac- tory area in the cortex causes almost exactly the same re- sult, viz., anosmia in the same side of the nose. The ol- factory path is,- chiefly, if not entirely, uncrossed. (c) In the Jiippocampus major are five layers of cortical matter, which represent the first four of typical cortex. The first layer, the one bounding the dentate fissure, is the invo- luted medullary lamina. This is the regular network of medullated fibers, but is more highly developed than in typi- cal cortex. It is just beneath the pia, a little neuroglia only intervening. The second layer is composed of closely packed small cell-bodies (granules). It is the stratum granulosum. There are no neurone-centers in the third layer, but a dense network of pyramid and granule dendrites. The first three layers represent the neurogliar layer of typical cortex. The fourth is a very thick layer and is made up of pyramids of medium size. To the fourth layer the second and third lay- ers in typical cortex correspond. The medullated axones of the pyramids constitute the thin lamina of white matter called the alveus which forms the ventricular surface of the hippocampus major. Fifth. — ^Between the alveus and the pyramids is a thin polymorphous layer, which resembles the fourth layer of parietal cortex. (d) The fourth exception to the typical cortex is found in 76 THE BRAIN AND SPINAL CORD. the floor of the fissure of Sylvius. It consists of a very great thickening of the fusiform layer. All five laminae are pres- ent. This cortex resembles the claustrum. The claustrum (a rampart) is an isolated sheet of gray matter, in structure much like the fifth layer of the cortex. It is cortical matter, according to Meynert. It is a vertical antero-posterior sheet placed medial to the island of Eeil, and lateral to the external capsule. The surface in contact with the external capsule is smooth, but the external surface is convoluted to coincide with the gyri insulse. At its lower border it Joins the lenticular nucleus. It is made up of fusi- form cell-bodies, which lie between the fibers of the uncinate fasciculus (see below — association fibers). II. Ganglionar Gray Matter. w It is found in the great ganglia which have already been considered. They should be re-studied in this connection. They are as follows : 1. In the hemisphere: Corpus striatum, composed of the caudate and the lenticular nucleus. 2. In the inter-brain : The optic thalamus, the external geniculate body, nucleus Luysi and red nucleus. 3. In the mid-brain: The internal geniculate body, the anterior and the posterior quadrigeminal body, a lateral half of the substantia nigra, and other less important nuclei in the tegmentum. The corpus striatum is an ovoid mass of reddish-gray mat- ter containing pigmented multipolar cell-bodies of various sizes, those of large size being more numerous in the nucleus THE GRAY AND WHITE MATTER. ']'] lenticularis than in the nucleus ccmdcdus. The axones of those cell-bodies run both toward the pons and toward the cerebral cortex. The corpus striatum, therefore, forms a way-station in an efferent conduction tract and, perhaps a less important one, in an afferent tract. Of the Centrifugal Fibers note the following three bundles : (a) A large bundle of axones from the striate body, the intermediate tract, runs down through the internal capsule and crusta to the nucleus pontis. It forms a thin inter- mediate zone between the pyramidal tract and substantia nigra in the mid-brain. Axones from the nucleus pontis continue the tract to the cerebellum (Flechsig). (b) Eding- er's bundle rises in the caudate nucleus and in the putamen of the lenticular nucleus and, running through the anterior segment of the internal capsule, terminates in the optic thalamus, chiefly; but also in the substantia nigra and inferior quadrigeminal body, (c) The centrifugal axones of the ansa lenticularis. They rise principally from the puta- men of the lenticular nucleus. After running through the medullary lamina of that nucleus they proceed medialward beneath the globus pallidus. The greater number end in the nucleus of Luys; certain others terminate in the optic thal- amus and the remainder in the tuber cinereum and gray mat- ter in the lateral wall of the third ventricle. The best known Centripetal Fibers received by the corpus striatum are (a) certain fibers of the medial fillet contained in the ansa lenticularis, and (b) the olivary bundle (Flech- sig). They arborize about the cell-bodies in the globus pallidus, whence other axones rise and continue to the somaes- thetic area of the cerebral cortex. Lesions of the corpus striatum affect the internal capsule and may cause, if extensive, hemiplegia and hemianesthesia 78 THE BRAIN AND SPINAL CORD. of the opposite side of the body and partial deafness chiefly in the opposite ear and hemianopia of the corresponding halves of both retinae. The optic thalanms^ is made up chiefly of gray matter containing multipolar and fusiform cell-bodies. The white matter, the internal medullary lamina, divides the gray into nuclei, of which Nissl has described about twenty. They may be grouped as follows: (1) The internal, or medial, nucleus is joined to the opposite inner nucleus by the gray (or middle) commissure and is continuous with the gray matter in the wall and floor of the third ventricle; but the internal medullary lamina separates it from the other nuclei of the same thalamus. (3) The external, or lateral, nucleus is the largest. It extends from dorsal to ventral surface the entire length of the thalamus (Burdach). It forms the terminal nucleus for the larger part of the tegmental fibers and the nucleus of origin for most of the fibers of the ansae peduncularis et lenticularis and anterior stalk of the thalamus. Destruction of this nucleus interrupts the common sensory path, and causes hemianesthesia of the opposite side. (3) The nucleus of the anterior tubercle, or anterior nucleus, receives the anterior pillar of the fornix through the bundle of Vicq d^Azyr. (4) The posterior nucleus is a small one. It is situated under the pulvinar between the geniculate bodies. (5) The nucleus of the pulvinar is an important one. It receives about twenty per cent of the optic fibers and gives rise to a corresponding number of the afferent fibers in the optic radiations to the occipital lobe, hence a lesion of the pulvinar impairs vision. (1) Thalamus. THE GRAY AND WHITE MATTER. 79 (6) The nucleus of the habenula belongs to the epithala- mus. It lies beneath the trigonum habenulse. It receives fibers from the rhinencephalon through the pineal stria, also fibers from the optic tract, and originates a bundle of fibers, fasciculus retroflexus (Meynert), which may be traced back through the tegmentum to the interpeduncular ganglion in the substantia nigra. (7) The central nucleus (center median of Luys) is situated deep in the thalamus below and between the internal and external nuclei and dorsal to the red nucleus. It gives origin to some fibers of the ansa lenticularis which run to the cortex. \. ■ . v- . The white matter of the optic thalamus has, for the most part, an indefinite arrangement. Into it enter the tegmental and fillet fibers and end, chiefly, in the lateral nucleus. It also receives axones or collaterals from every part of the cerebral cortex and sends fibers to the somaesthetic and spe- cial sense areas. The white matter forms the S-shaped in- ternal medullary lamina and is continued in numerous bundles of fibers which enter the hemisphere. These bundles are as follows: (1) The anterior pillar of the fornix, having pierced the thalamus, descends to the corpus albicans, while the bundle of Vicq d'Azyr,2 which rises there, ascends to the thalamus and terminates in its anterior nucleus. (2) From the external surface two groups, which rise chiefly in the lateral nucleus, proceed into the cortex of the general sensory region (the somaesthetic area) : (a) The in- ferior is the ansa peduncularis. It passes below the lenticular nucleus with the internal capsule, and enters into both the medullary laminae of that nucleus and the external capsule. (2) Fasciculus mamlllaris. 80 THE BRAIN AND SPINAL CORD. It ends chiefly in the cortex of the ascending frontal and ascending parietal convolutions. Its fibers are medullated at the beginning of the ninth month (Flechsig). (b) The superior group is the ansa lenticularis, which pierces the superior lamina of the internal capsule and then the nucleus lenticularis, where some of its fibers are interrupted. It assists in forming the external capsule and ends in the cen- tral gyri, the paracentral lobule, the foot of the superior frontal convolution and the entire limbic lobe. The fibers of the ansa lenticularis become medullated at the end of the ninth month (Flechsig). (3) The anterior stalk streams from the anterior end of the lateral nucleus, via the frontal segment of the internal capsule, into the frontal lobe. The fibers of the stalk end in the cortex at the foot of the inferior and middle frontal gyri, the anterior half of the superior frontal convolution and the middle of the gyrus fornicatus. Its fibers receive their medullary sheaths near the end of the tenth month (Flechsig). From the same part of the cerebral cortex the frontal cerebro-corticopontal tract rises. The ansae peduncularis et lenticularis and the anterior stalk of the thalamus are called the cortical fillet; they carry ordinary sensations, chiefly from the fillet and superior cere- bellar peduncles, up to the somaesthetic cortex. Interruption of the cortical fillet stops all common sensory impulses. (4) A large pencil of fibers, the optic radiations,^ passes from the pulvinar and external geniculate body through internal capsule to the visual centers in the occipital lobe. A number of the optic radiations are efferent and end in the superior quadrigeminal body. Destructive lesion of the optic radiations of either side produces hemianopia of the same side of both retinae. (3) Radiatio occipitothalamica. THE GRAY AND WHITE MATTER. 8 1 (5) Another pencil of fibers radiates from the region of the internal geniculate body through internal capsule to the jiuditory area in the temporal lobe. It constitutes the acustic radiations^ If the acustic radiations be destroyed the result is partial deafness affecting chiefly the opposite ear. The red nucleus^ of the tegmentum is situated beneath the optic thalamus. It is a way-station in the indirect sen- sory tract, receiving the opposite superior cerebellar peduncle and, by its axones, continuing the tract to the optic thalamus and somaesthetic cortex. It also receives efferent axones and gives origin to two bundles: (a) One centrifugal bundle of axones (the crossed descending tract), after crossing over in the tegmentum, descends, first, with the medial portion of the lateral fillet; second, through the lateral area of the medulla, and, third, through the dorso-lateral part of the crossed pyramidal tract in the spinal cord. Gradually di- minishing, it disappears at the first lumbar segment. It ends in the lateral horn and center of the gray crescent of the spinal cord, (b) The red nucleus also sends a bundle of axones through the opposite superior peduncle of the cere- bellum to the corpus dentatum. The nucleus hypothalamicus (Luysi) is a pigmented bi- convex mass of gray matter placed ventro-lateral to the red nucleus, and between it and the fibers of the crusta. It constitutes an important relay for certain fibers of the medial fillet. Certain descending fibers from the striate body termi- nate in this nucleus. It is also Joined to the lamina cinerea and tuber cinereum by a bundle of fibers that accompanies Gudden's commissure along the medial part of the optic tract. This bundle constitutes Meynert's commissure. (4) Radiatio temporothalamlca. (5) Nucleus ruber. 82 THE BRAIN AND SPINAL CORD. The external geniculate lody,^ which receives eighty per cent of the optic fibers (Von Monokow) and forms a relay in the optic path, and the internal geniculate hody,'^ which is a way-station in the auditory tract, have been sufficiently described. Ablation of the former interrupts the optic path, and of the latter the auditory path. The superior pair of the corpora quadrigemina^ represent the corpora bigemina, the optic lobes, of birds, fishes and reptiles. They are composed of three laminae: (1) The superficial white matter, the stratum zondle. That layer with the fibers of the interior is continuous, through the superior brachium, with the optic tract and radiations. Many of them are crossed fibers. (2) The stratum cinereum forms a cap of gray matter beneath the stratum zonale. In struc- ture it resembles the gray substance of the inferior bodies. (3) Its multipolar cell-bodies increase in size toward the second gray layer, the stratum opticum. In that, the cell- bodies are very large. They are grouped in masses between the abundant fibers from the outer root of the optic tract, which arborize about them. They give rise to axones which associate the optic fibers with the nuclei of the third, fourth and sixth cranial nerves, and with the cilio-spinal center in the cervical cord. The stratum opticum rests upon the quad- rigeminal lamina. Some gray matter is scattered through the latter, and Tartuferi calls it the "stratum lemnisci/' The superior quadrigeminal body forms a terminal nucleus for certain fibers of the superior lemniscus, which bring to it ordinary sensations from spinal and cranial nerves. A bundle of fibers (the anterior longitudinal bundle) rises from the superior quadrigeminal body, and descends along (6) Corpus geniculatum lateraJe. (7) Corpus geniculatum mediale. (8) Colliculi anteriores corporum quadrigeminorum. THE GRAY AND WHITE MATTER. 83 the ventral surface of the opposite posterior longitudinal bundle to the anterior cornu of gray matter in the spinal cord. This bundle rises in relation with the optic fibers and ends in the cilio-spinal center, which gives origin to white rami communicantes, and in other motor centers. It forms one segment of a reflex arc concerned in dilating the pupil. Destructive lesions affecting the superior quadrigeminal bodies produce loss of reflex movement of the eyeballs, loss of pupillary reflex and loss of accommodation. In the inferior pair of the quadrigeminal bodies^ the white fibers are continuous, behind, with the lateral fillet ; and with the inferior brachium, antero-externally. The deep part of the inferior bodies is gray matter. It contains a network of fine fibers, and small multipolar cell-bodies.' The latter are in relation with the terminal end-tufts of the lateral (lower) fillet fibers, and give origin to the fibers of the inferior brach- ium. The inferior bodies are united beneath the sulcus longi- tudinalis both by decussating fibers of the fillet and by gray matter. In distinction from the superior bodies, the inferior pair may be called the. auditory lobes ; they are well marked only in those mammals having highly specialized organs of hearing, and form an important way-station in the auditory conduction path, hence their destruction causes the same symptoms as interruption of the acustic radiations, namely, deafness affecting chiefly the opposite ear. Substantia Nigra. — The small pigmented multipolar cell- bodies which make up the substantia nigra form, first, a terminal nucleus for certain fibers of the medial fillet and a nucleus of origin for other fibers which continue in that tract (Barker) ; and, second, a terminal way-station for the fasciculus retroflexus of Meynert and for certain flbers of (9) Colliculi posteriores corporum quadrigeminorum. 84 THE BRAIN AND SPINAL CORD. Edinger^s bundle from the corpus striatum (see pages 77, 79). Beyond this terminal station the efferent tracts are probably continued, but they have not been traced. III. Central, or Ventricular, Gray Matter. It is located (1) in the floor and walls of the third ven- tricle, (2) in the middle commissure of that ventricle, and (3) around the Sylvian aqueduct. (1) The lamina cinerea and tuber cinereum form a sheet of gray substance that connects the inferior surfaces of the hemispheres and may be called their inferior (or great) gray commissure. From the floor of the third ventricle it extends laterally beneath the optic thalamus, and is continuous with the anterior perforated lamina. The gray matter of the floor extends up a short distance on the medial surface of the thalamus opticus; and in that upturned part is located the anterior end of the motor oculi nucleus. The inferior gray commissure receives efferent fibers through the ansa lenticu- laris from the corpus striatum, and is joined to the nucleus of Luys by the fibers of Meynert's commissure. (2) The middle commissures^ joins the internal nuclei of the optic thalami. It is continuous with this upward exten- sion of the gray floor of the third ventricle. In the middle commissure are cell-bodies and transverse fibers. The latter appear to be loops which reach only to the median line; at least many of the fibers do not cross to the opposite side. (3) The nuclei of the oculomotor (third) and of the trochlear (fourth) cranial nerves are found in the gray mat- ter about the Sylvian aqueduct. In it also is a part of the motor nucleus of the trigeminal, or fifth, nerve. Lesions which involve the trochlear and oculomotor nuclei, as a rule, (10) Massa intermedia. THE GRAY AND WHITE MATTER. 85 also involve the fibers of the tegmentum, and the result is ocular paralysis on the same side and impaired sensation (hemiataxia) on the opposite side of the body. The white matter of the cerebrum and mid-brain is com- posed of three definite systems of fibers: 1. Projection, or peduncular, fibers. 2. Transverse, or commissural, fibers. 3. Association fibers. I. Projection Fibers. They are composed, first, of the medullated axis-cylinders of the large and medium-sized pyramids and of a few of the polymorphous neurones in the cerebral cortex; and, second, of medullated axones of neurones whose centers are situated in masses of gray matter below the cerebral cortex. The projection fibers are therefore both centrifugal and centripe- tal. They run through the mid-brain to the cerebral cortex and vice versa, connecting the cortex, directly or indirectly, with all parts of the body, throwing or projecting a picture of every part and organ upon the cerebral cortex. Many of the fibers are interrupted in the basal ganglia, especially of ihe centripetal fibers. Within the hemisphere the projection fibers help to form the centrum semiovale and the corona radiata and then, converging, form the internal capsule. More distally, in the mid-brain, they are divided into two great groups of fibers, the crusta and the tegmentum, sepa- rated by the substantia nigra. CENTRIFUGAL, OR MOTOR, PROJECTION FIBERS. The Crustae comprise most of the centrifugal, or motor, fibers, namely, the intermediate bundle, the frontal cerebro- corticopontal tract,^^ the p3rramidal tract and the temporal (11) Tractus cerebro-corticopontalis frontalis. 86 THE BRAIN AND SPINAL CORD. cerebro-corticopontal tract.^^ The intermediate tract extends from the corpus striatum through the deep part of the crusta to the motor cranial nuclei and to the nucleus pontis, whose axones run by way of the middle cerebellar peduncle to the cortex of the opposite hemisphere of the cerebellum. It thus forms a segment of an indirect (through the cerebellum) efferent, or motor, path. The fronto-pontal tract^^ rises from the feet of the second and third frontal gyri and the anterior half of the first frontal gyrus and from the middle of the gyrus fomicatus. It traverses the centrum semiovale, corona radiata, anterior segment of the internal capsule and internal one-fifth of the crusta to the ventral area of the pons, where it terminates in the nucleus pontis (chiefly) and in the nuclei of motor cranial nerves (Flechsig). According to Dejerine, the temporo-pontal tract^^ extends from the temporal lobe through the inferior lamina (and posterior part of the superior lamina) of the internal capsule and outer one-fifth of the crusta to the same nucleus; but according to Spitzka some of its fibers end in nuclei of motor cranial nerves. Thus it should be noted that, with the exception of those fibers to motor nuclei of the cranial nerves, each of the three tracts above mentioned — viz., the intermediate, fronto-pontal and temporo-pontal — constitutes a segment of an indirect efferent path which is interrupted in the nucleus pontis and then con- tinued by the axones of that nucleus through the middle peduncle of the cerebellum. Axones from the Eolandic cortex constitute the Pyramidal Tract.13 Descending through the centrum semiovale, corona radiata, genu and anterior two-thirds of the posterior segment of the internal capsule, the pyramidal tract comprises the (11) Tractus cerebro-corticopontalls frontalis. (12) T. cerebro-corticopontalis temporalis. (13) Fasciculus longitudinalis (pyramidalis) pontis. THE GRAY AND WHITE MATTER. 8/ middle three-fifths of the crusta, the ventral longitudinal fibers of the pons, the pyramid of the medulla and the crossed and uncrossed pyramidal tracts of the spinal cord. The fibers of the pyramidal tract, with a few exceptions, cross over to the opposite side; they end in the motor nuclei of cranial and spinal nerves. Fibers enter the nucleus of the trochlear (or fourth cranial) nerve on the same side and a few descend to the motor nuclei of other cranial nerves and to the anterior cornu of gray matter in the spinal cord with- out decussation; all other pyramidal fibers terminate on the side opposite to their origin. Cranial fibers. — Those fibers of the pyramidal tract which end in the nuclei of cranial nerves rise in the lower (two-fourths) and anterior part of the Eolandic, or motor, area, including also that part of the marginal convolution situated above the genu of the corpus callosum. They run through, the genu of the internal cap- sule and, chiefly, through the inner portion of the middle three-fifths of the crusta ; a considerable number run through the outer portion of the pyramidal area. They terminate in the motor nuclei of cranial nerves. Upper extremity fibers. — The fibers of the pyramidal tract that end in the cervical part of the spinal cord, and through it innervate the muscles of the upper extremity, take their origin from that part of the central convolutions (third fourth) adjacent to the foot of the middle frontal gyrus, the foot of the superior frontal gyrus and the adjoining part of the marginal gyrus next behind the head center and directly above the anterior part of the truncus corporis callosi. These fibers run through the posterior segment of the internal capsule just behind the genu, and through the crusta immediately external to the cranial fibers. Those fibers which innervate the muscles of the thumb, fingers and hand, rise lowest down in the arm 88 THE BRAIN AND SPINAL CORD. area of the cortex and occupy the posterior part of the arm bundle in the internal capsule and the external part of it in the crusta. The fibers which control the shoulder muscles rise in the upper part of the cortical area and form the anterior and internal part of the arm bundle in the capsula interna and crusta, respectively, while the wrist, fore-arm, elbow and arm are innervated by means of fibers which are intermediate in both origin and course. Trunk fibers. — The trunk fibers of the pyramidal tract rise in the superior fourth of the ascending frontal gyrus and in the contiguous part of the marginal convolution immediately in front of the para- central lobule. In the internal capsule the trunk fibers run just behind those to the fingers and just external to them in the crusta. Lower extremity fibers. — A large number of the pyramidal fibers terminate in the lumbar enlargement of the spinal cord and carry impulses to the nerves of the lower extremity. They originate in the upper fourth of the as- cending parietal convolution, in the superior parietal gyrus and in the paracentral and quadrate lobules. The hip fibers rise farthest forward and the toe fibers farthest iDackward, immediately in front of the parieto-occipital fissure. The fibers have the same relative position in the internal capsule ; in the crusta the hip fibers are internal and the toe fibers external. Fibers which innervate the muscles of the thigh, leg and small toes have this same relative position and order between the hip and great toe fibers both in their cortical origin and in their course through the internal capsule and crusta. Several bundles of centrifugal fibers are found in the teg- mentum, namely, the anterior longitudinal bundle, the crossed descending tract of the red nucleus, a small part of the supe- rior peduncle of the cerebellum, the descending root of the THE GRAY AND WHITE MATTER. 89 trifacial nerve and certain fibers in the formatio reticularis. With these exceptions the tegmentum is centripetal, or sen- sory. Destruction by clot, tumor, or otherwise, of any of the above motor tracts causes (upper segment) paralysis of the particular muscles innervated through that tract. CENTRIPETAL, OR SENSORY, PROJECTION FIBERS. The sensory fibers of the tegmentum comprise the olivary bundle, the fillets, the optic tract (outer root), and the greater part of the posterior longitudinal bundle and superior cerebellar peduncle; perhaps, also, certain fibers in the for- matio reticularis. Excepting a small number of fibers, all these bundles terminate in the basal ganglia; but the paths of conduction are continued through the internal capsule. In the capsula interna the centripetal projection fibers con- stitute the three systems of Flechsig (the cortical fillet) and the optic and aeustic (and gustatory?) radiations. The former end in the somgesthetic area of the cerebral cortex, the latter in the visual, auditory and gustatory cortex. The exact origin of the Three Systems of Flechsig has not been determined, but they are known to rise, chiefly, in the lateral nucleus of the optic thalamus. The ansa peduncularis (first system of Flechsig) runs through the internal capsule behind the pyramidal tract in the inferior lamina. Some of its fibers enter the medullary laminae of the nucleus lenticu- laris and others enter the external capsule; ultimately they all terminate in the central convolutions. The ansa lenticu- laris (second system of Flechsig) issues from the lateral surface of the thalamus higher up than the former loop and mingles with the pyramidal fibers in the internal capsule. A number of its fibers pierce the internal capsule (superior QO THE BRAIN AND SPINAL CORD. lamina) and are interrupted in the lenticular nucleus; they assist in forming the medullary laminae of that nucleus and form a part of the external capsule. The lenticular loop terminates in the upper part of the central convolutions, the foot of the superior frontal gyrus, the paracentral lobule and the entire limbic lobe. From the anterior end of the optic thalamus streams a great pencil of fibers, called the anterior stalk (third system of Flechsig). It mingles to a small ex- tent with the fibers of the pyramidal tract, but runs chiefly through the anterior segment of the internal capsule. The anterior stalk terminates in the feet of the inferior and middle frontal convolutions, in the anterior half of the su- perior frontal gyrus and in the middle of the gyrus f ornicatus. The three systems of Flechsig convey common sensory im- pulses to the somsesthetic area of the cerebral cortex. They are often called the cortical fillet. If the cortical fillet be severed, all common sensory im- pulses to that hemisphere are interrupted and complete loss of sensation on the opposite side of the body (hemiataxia) results. The Acustic Radiations and the Inferior Brachium con- tinue the auditory path from the end of the lateral fillet, in the inferior quadrigeminal body, to the internal geniculate body and then, through the retrolenticular part of the internal capsule, to the transverse temporal gyri and the third and fourth fifths of the superior temporal convolution (Barker). Interruption of these fibers produces deafness in the opposite ear, which is not complete because the acustic path is not wholly crossed. The Optic Radiations rise in the external geniculate body and in the pulvinar of the optic thalamus. They continue the visual conduction path through the retrolenticular region THE GRAY AND WHITE MATTER. QI of the internal capsule to the cortex of the cuneate lobe. Half-blindness in the same side of both retinae results from section of the optic radiations. II. Commissural Fibers. They connect opposite sides of the cerebrum. They are contained chiefly in the corpus callosum, the anterior commis- sure, and the commissura hippocampi (N. 7, Add.). The Corpus Callosum is the great link between the hemi- spheres. Its fibers connect both similar and dissimilar parts of the cortices. It is made up of cortical axones, a few of them being projection fibers; and collaterals from the asso- ciation and projection fibers. All callosal fibers, except the few peduncular fibers, end on the opposite side in arboriza- tions within the cortex. The Anterior Commissure joins the opposite temporal and occipital lobes together (pars occipito-temp oralis) ; and the limbic lobes with each other and with the contra-lateral olfactory tract (pars olfactoria). The Commissura Hippocampi, the lyre, unites the hippo- campus major, the uncus and the optic thalamus with their fellows of the opposite side. III. Association Fibers. These fibers remain on the same side and connect parts of the same hemisphere. They are situated within or close to the cortex, the various parts of which they serve to unite. The Short Association Fibers are probably the axones of the irregular cell-bodies (Cajal's) situated in the neurogliar layer of the cortex. They unite contiguous parts of the same convolution and associate together adjacent convolutions. They comprise arcuate and tangential fibers. They are the more numerous and very important. Among them are fibers 92 THE BRAIN AND SPINAL CORD. which connect the visual sensory area with the visual mem- ory area and the auditory sensory with the auditory memory area. Interruption of these association fibers gives rise to certain forms of sensory aphasia (N. 4, Add.). The Long Association Fibers are collected into bundles. The long association fibers rise chiefly from the polymorph- ous and fusiform layers of the cerebral cortex, but also, to some extent, from the pyramids in the second and third layers (Cajal). They are axones. Proceeding out of the lobe in which they rise, they arborize about neurones in more or less distant parts of the cortex. The long association fibers dip down into the centrum semiovale and bring into harmonious action the widely separated cerebral centers. Among the best known are the following bundles: (1) The Cingulum, or the fillet of the gyrus fornicatus, is a bundle of fibers in the falciform gyrus (the fornicate and hippocampal gyri), which almost entirely encircles the cor- pus callosum. It extends from the anterior perforated lamina, through the gyrus fornicatus and hippocampal con- volution, to the uncus. The fibers have been divided into three groups by Beevor, namely: (a) The anterior, which joins the anterior perforated lamina and internal olfactory root to the fore part of the frontal lobe, (b) The horizontal, which unites the frontal lobe and the gyrus fornicatus. And (c) the posterior fasciculus, which associates the lingual and fusiform gyri with the hippocampal gyrus and pole of the temporal lobe. (2) The Fornix. — Each lateral half of the fornix^* is a bundle of association fibers. Its anterior end (or pillar) is connected with the corpus albicans; and, through the bundle of Vicq d'Azyr, also with the optic thalamus. The posterior (14) Corpus fornicis. THE GRAY AND WHITE MATTER. 93 pillar, descending in the middle horn of the lateral ventricle, for the most part, disappears in the hippocampus major (its origin) ; but a small bundle of its fibers, constituting the corpus fimbriatum, continues to the uncus. (3) The Uncinate Fasciculus is a bundle,^^ with some sharply curved fibers, which arches over the main stem of the Sylvian fissure, and connects the uncus and the orbital part of the frontal lobe. It is situated near the basal surface. Its fibers spread out at both ends in the cortex, and they espe- cially join the internal and posterior orbital and the third frontal convolution with the limbic lobe (Barker). Like the cingulum and fornix, it is connected with the rhinencephalon. Lesion in any one of these three bundles causes disturbance of smell. (4) The Superior Longitudinal Fasciculus'^^ is a sagittal bundle located beneath the convex surface of the hemisphere, just above the horizontal ramus of the fissure of Sylvius. It joins the frontal cortex with the parietal and the external temporal. It thus associates the auditory and the visual mem- ory centers with the motor speech center; hence, aphasia is the result of its interruption. (5) The Inferior Longitudinal Fasciculus'^'^ is about on a level with the lateral ventricle. It passes near the outer wall of the descending and posterior cornua of that ventricle, and connects the temporal lobe to the occipital. In the temporal lobe its fibers cross at right angles those of the inferior lamina of the internal capsule. This fasciculus unites the auditory and visual memory centers, and thus associates the memories of things seen with the memories of things heard. (6) The Fasciculus Occipito-frontalis (Forel). — This is (15) Fasciculus uncinatus. (16) Fasciculus longitudinalis superior, (17) Fasciculus longitudinalis inferior. 94 THE BRAIN AND SPINAL CORD. a large bundle of fibers formerly regarded as a part of the corpus eallosum. It is situated between the cingulum and the superior longitudinal bundle. Just external to the lateral ventricle. It extends from the cortex of every part of the frontal lobe to the cortex of the convex surface and lateral border of the occipital lobe. Posteriorly, the fibers diverge to form a fan-like sheet, and that sheet enters into the ex- ternal boundary of the descending horn of the lateral ventricle and into the fioor, lateral wall and roof of the posterior horn, hence the synonym, tapetum. Its particular function is un- known. (7) The Perpendicular Fasciculus}^ — This is a very broad vertical bundle located just in front of the occipital lobe. Anteriorly, it extends from the inferior parietal con- volution, above, down to the second and third temporal ; and, posteriorly, it joins the superior occipital convolution with the middle and inferior occipital and with the fusiform gyrus of the temporal lobe. Its function is doubtful. NOTE. The student will find many obscure points cleared up by a careful study of the embryology of the cerebrum (see Chap. XI., page 202). BLOOD SUPPLY OP THE CEREBRUM AND MID-BRAIN. The blood supply of the cerebrum and mid-brain is de- rived from the anterior choroid and the anterior and middle cerebral arteries, all branches of the internal carotid; and from the posterior cerebral arteries, which are terminal branches of the basilar artery. They form a remarkable anastamosis at the base of the brain, the circle of Willis.^ ^ The Circle of Willis (really a heptagon) extends from a (18) Fasciculus perpendicularis. (19) Cireulus arteriosus. THE GRAY AND WHITE MATTER. 95 point in the great longitudinal fissure, anterior to the optic commissure, back to the pons. It is about an inch and a half long, and one inch in transverse diameter. In front are the anterior cerebral arteries converging forward from the internal carotids and uniting through the anterior communi- cating artery.2<^ The posterior communicating artery^^ forms the lateral boundary of the circle. It forms the anastamosis between the internal carotid artery and the posterior cere- bral. The posterior cerebral arteries bound the circle be- hind. The superior cerebellar arteries send several branches to the dorsum of the mid-brain. The large distal 'branches of the cerebral arteries are dis- tributed chiefly to the cortex and medulla of the hemispheres ; while the small proximal hranches supply the ganglia and inter-brain. The former belong to the cortical system, the latter to the ganglionic system. CORTICAL SYSTEM. The Anterior Cerebral Artery22 enters the great lon- gitudinal fissure. Winding aronnd the genu of the corpus callosum, it runs back on the medial surface of the hemi- sphere to the parieto-occipital fissure. It has three branches : (1) Anterior internal frontal, which supplies the internal orbital convolution and olfactory bulb, the superior frontal and the anterior half of the middle frontal gyri. (2) Mid- dle internal frontal, which is distributed to the corpus cal- losum, gyrus fornicatus, marginal convolution and upper end of the ascending frontal convolution. And (3) Posterior internal frontal, which supplies the quadrate lobe and part of the superior parietal convolution. The Middle Cerebral Artery23 runs in the fissure of Sylvius. It has four distal branches : (1) External and infe- (20) A, communicans anterior. (22) Artera cerebri anterior. (21) A. communicans posterior. (23) Artera cerebri media. g6 THE BRAIN AND SPINAL CORD. rior frontal, to the anterior and posterior orbital and third frontal convolutions; (2) Ascending frontal, and (3) As- cending parietal, to convolutions of the same name. The ascending frontal also supplies the foot of the middle frontal gyrus; and the ascending parietal artery, a part of both the superior and inferior parietal convolutions. And (4) Parieto- temporal, which supplies the supragmarginal and the angular and the superior and middle temporal gyri. The Posterior Cerebral Artery,^* winding from the basilar artery25 outward around the mid-brain, breaks up into three cortical branches on the tentorial surface of the hemisphere. Their distribution is as follows : ( 1 ) Occipital, to the cuneus and the convex surface of the occipital lobe; (3) Uncinate, to the same convolution (hippocampal and lingual), and (3) Temporal (or temporo-sphenoidal), to the fourth, third and part of the second temporal gyri. These vessels of the cortical system and their many branches pierce the hemispheres perpendicular to the surface. They are distributed, the short, to the cortex, and the long, to the medulla of the hemispheres. To a limited extent they anastamose with one another, but they do not communicate with the ganglionic system. GANGLIONIC SYSTEM. Small arteries from the circle of Willis and from the cere- bral arteries near the circle constitute this system. It is made up of six groups of vessels: (1) Antero-median Granglionic. — They rise from the an- terior cerebral arteries and anterior communicating. Piercing the lamina cinerea (and a few of them, the anterior perfo- rated lamina) they supply the bulb of the caudate nucleus and anterior wall of the third ventricle. (24) Artera cerebri posterior. (25) A. basilaris. THE GRAY AND WHITE MATTER. 97 (2, 3) The Antero-lateral Ganglionic Arteries take their origin, on either side, from the middle cerebral artery, a little outside the circle of Willis. They pierce the anterior perfo- rated lamina and are distributed to the striate body, internal capsule and optic thalamus. One of this group is the len- ticulo-striate artery. It supplies almost the entire corpus striatum. On account of its frequent rupture, it is called the artery of cerebral hemorrhage ( Charcot) . (4) Postero-median Ganglionic. — These are branches of the posterior cerebral and posterior communicating arteries. They supply the interpeduncular structures and crustae ; and (after piercing the posterior perforated lamina) the walls of the third ventricle and medial parts of the optic thalami. (5, 6) Postero-lateral Ganglionic Arteries. — They rise, on either side, from the posterior cerebral artery after it has wound around the crusta. They are distributed to the pos- terior part of the optic thalamus, the geniculate bodies and corpora quadrigemina. The ganglionic arteries pass to their distribution without communicating with one another or with the cortical arteries. They are end-arteries of Cohnheim. Between the cortical and ganglionic systems, there is an area:^ poorly supplied with blood. That is the area of cerebral softening. Choroid Arteries.^^ — They are three in number. Anterior Choroid. — Coming from the internal carotid ar- tery, the anterior choroid artery^^ enters the apex of the descending horn of the lateral ventricle; and supplies the inferior two-thirds of the choroid plexus, a part of the velum interpositum, the hippocampus major and corpus fimbriatum. The Postero-lateral ChoroidJ^^ is a branch of the posterior (26) Arterise choroidese. (27) Arteria choroidea anterior. : , (28) A. choroidea postero-lateralis. I ; 98 THE BRAIN AND SPINAL CORD. cerebral. It is distributed to the upper third of the choroid plexus of the lateral ventricle and to the velum interpositum. Poster o-medial Choroid?^ — ^Also a branch of the posterior cerebral artery, it supplies the choroid plexuses of the third ventricle; and, with branches from the superior cerebellar, completes the supply of the velum interpositum. The pos- tero-lateral and postero-medial choroid vessels have their origin, course and distribution wholly within the great trans- verse and choroid fissures. Veins.3^ — ^The velum interpositum and lateral and third ventricles are drained by the common vein of Galen.^^ The veins of Galen (Vv. cerebri intemse) are formed, one on either side, at the foramen of Monro, by the union of the veins of the striate body^^ q^^^ choroid vein and receive the basilar.33 The Supenor Cerebral Veins,^^ eight to twelve in number, carry away the blood from the superior surface of the hemi- sphere. They run obliquely upward and forward into the superior longitudinal sinus.^^ Just before emptying into the sinus they receive most of the medial veins.^^ , The Medial Cerebral Veins. — They drain the medial sur- face of the hemisphere. The veins of that surface which do not empty into the superior cerebral veins unite and form the inferior longitudinal sinus-^*^ The base of the cerebrum and border of its convex surface are drained by the Inferior Cerebral Veins. ^^ On the tento- (29) Arteria choroidea postero-medialls. (30) Venae. (31) V. cerebri magna. (32) V. corporis striati (sing.). (33) V. choroidea. \ (34) W. cerebri superiores. (35) Sinus sagittalis superior. (36) Vv. cerebri medlales. ' (37) Sinus longitudinalis inferiof. (38) Vv. cerebri inferiores. ' THE GRAY AND_WHITE MATTER. 99 rial surface of the hemisphere, these veins empty, against the current, into the lateral and superior petrosal sinuses.^^ Those from the temporal and frontal lobes empty into the cavernous sinus,^^ excepting the small anterior cerebral vein and the deep Sylvian vein, which unite with the inferior striate veins in forming the basilar. The basilar vein receives additional blood from the interpeduncular structures, the uncinate gyrus and the middle horn of the lateral ventricle and from the mid-brain as it winds around it to empty into the corresponding vein of Galen near its termination. In or near the fissure of Sylvius there are two inferior cerebral veins of large size: The middle cerebral vein/'^ which runs from the under surface of the temporal lobe, medialward, along the fissure of Sylvius to the cavernous sinus; and the great anastamotic vein of Trolard, whose course is much the same, but in front of, the Sylvian fissure. Rising on the parietal lobe, it winds inward along the lesser wing of the sphenoid bone to the anterior extremity of the cavernous sinus. The main trunks of all the cerebral vessels are con- tained in the pia mater. There are no lymphatic vessels in either the brain or spinal cord; perivascular lymph spaces carry the fluid from the interior to the subarachnoid spaces. (39) Sinus transversus and S. petrosus superior. (40) Sinus cavernosus. (41) Vena cerebri media. CHAPTER V. HIND-BRAIN. Section I. The Cerebellum. The hind-brain is composed of the cerebellum and the pons. The cerebellum is the dorsal portion of the hind-brain. It is called the little brain. Its weight is about five ounces, slightly more than one- tenth of the whole brain. It is situ- ated in the posterior fossa of the skull, under the tentorium cerebelli and dorsal to the pons and medulla oblongata. Be- tween it and the last two structures is inclosed the fourth ventricle.^ Function. — The cerebellum is an important way-station, or relay, in the indirect motor and indirect sensory paths. In response to impulses received from skin, muscles, tendons, joints and viscera, it is also believed to originate impulses which co-ordinate muscles and maintain equilibrium. More- over, according to Russell, each cerebellar hemisphere exer- cises an important inhibitory function, through the superior peduncles, upon the opposite side of the cerebrum. Divi- sions. — The cerebellum is made up of two lateral parts, the hemispheres,^ and a central part, uniting the hemispheres together, called the vermis cerebelli, or worm. The Cerebellar Hemispheres measure two inches from be- fore backward and about the same in thickness, antero- medially; but they taper rapidly toward the lateral borders. (1) Ventriculus quartus. . , , , , (2) Ke^nlsphuerium ceretelli. '. / - , / '<■ \ ' HIND-BRAIN. lOI They are joined together by the worm, which forms the most elevated part of the cerebellum. The vermis, or worm, is a small elongated lobe, shorter and much thinner than the hemisphere. In animals" lower than mammals, it is the only part of the cerebellum present. Its transverse ridges give it a worm-like appearance. It unites the upper half of the medial aspect of the hemispheres, their lower halves being separated by an antero-posterior groove, called the valley, or vallecula.^ The upper surface of the vermis is called the superior worm, or vermis superior; and the lower surface, the inferior worm, or vermis inferior. The superior and inferior surfaces are separated from one another at the posterior end of the worm by the great hori- zontal fissure;* anteriorly, the medullary body^ of the cere- bellum separates them. At either end of the worm is a notch bounded by the vermis and the hemispheres, the anterior and posterior cerebellar notches. The posterior cerebellar notch, incisura cerebelli posterior, is occupied by the falx cerebelli. A prolongation of the medullary body of the cerebellum issues from the incisura cerebelli anterior, or anterior cerebellar notch. The Medullary Body splits, in its medial part, into two laminae: a superior, which forms the superior medullary ve- lum and three pairs of peduncles, and an inferior, which is the inferior medullary velum. Separating at an acute angle, the two laminae form the tent and lateral recesses of the fourth ventricle. The inferior medullary velum^ is the inferior lamina of the medullary body. It is a short plate of white matter, not (3) Vallecula cerebelli. <4) Sulcus horizontalis cerebelli. (5) Corpus medullare. (6) Velum medullare poaterius. 102 THE BRAIN AND SPINAL CORD. more than a quarter of an inch long. It ends in a concave border from which a sheet of epithelium continues down over the fourth ventricle; and together they form the inferior half of the roof of that cavity. Laterally, the inferior velum extends to the flocculus of the hemisphere, and blends with the middle cerebellar peduncle. Of the worm it covers the nodulus, antero-superiorly. It bounds, dorsally, the lateral recesses of the fourth ventricle. The Superior Lamina of the Medullary Body joins the cere- bellum immediately to the pons. The superior lamina is made up of three pairs of cerebellar peduncles and the supe- rior medullary velum.''' They are the prolongations of the white matter which constitutes the corpus medullare of the cerebellum. The superior peduncles (crura ad cerebrum, or brachia conjunctiva) converge as they pass forward and upward to the inferior quadrigeminal bodies, where they disappear. They are joined to one another by a thin plate of white matter, the superior medullary velum, or valve of Vieussens; with the valve, they form the dorsal longitudinal fibers of the pons ; and, as such, the roof and lateral boundaries of the superior half of the fourth ventricle. Beneath the corpora quadrigemina and aqueduct of Sylvius, most of the fibers of the superior cerebellar peduncles decussate, and pass into the hypothalamic region of the opposite side. They end chiefly in the red nucleus, which they surround. The inferior peduncles of the cerebellum (crura ad niedul- 1am) 8 issue from the cerebellum between the superior and middle peduncles. They first run ventrally to the dorsal surface of the pons, near the posterior border; and then, bending downward and backward (a flexion of more than 90 (7) Velum medullare anterius. (8) Corpora restlformia. HIND-BRAIN. IO3 degrees), they converge in the posterior areas of the medulla toward the calamus scriptorius. They help to form the floor and to bound laterally the inferior half of the fourth ven- tricle. In. the medulla they are called the restiform bodies. The middle peduncles (crura ad pontem)^ join the cere- bellum to the lateral borders of the pons. They are con- tinuous with the ventral (or superficial) transverse and the middle transverse fibers of the pons. The middle peduncles are external to the superior and inferior peduncles, and are opposite the widest part of the fourth ventricle. Great Horizontal Fissure. — The cerebellum has one great fissure which divides it into upper and lower surface. The sulcus horizontalis cerebelli is shaped like a horseshoe; its extremities are located on either side of the medullary body, from which the fissure runs backward, dividing the border of each hemisphere and the posterior end of the worm. In the great horizontal fissure the remaining important fissures of the cerebellum terminate. They are nearly parallel with one another; hence, the cerebellum is laminated, not convoluted like the cerebrum. The extremities of the great horizontal fissure are separated from the fourth ventricle by a sheet of epithelium, on either side, uniting the borders of the superior and inferior medullary laminae, and bounding externally the lateral recesses. When the cerebellum is separated from the pons and medulla it presents along its anterior border be- tween superior and inferior medullary laminae the transverse fissure. SUPERIOR SURFACE OF THE CEREBELLUM. The superior surface^^ of the cerebellum is bounded by the great horizontal fissure and the superior lamina of the medul- (9) Brachia pontis. (10) Fades cerebelli superior. 104 THE BRAIN AND SPINAL CORD. latry body. It is divided into five continuous lobes by four crescentic fissures, called interlobular fissures.^^ Fissures. — ^The interlobular fissures divide the worm and both hemispheres; and each lobe is composed of a central and two lateral portions, called lobules. These fissures are named in accordance with their relations to the lobules in the worm, viz.: (1) The Preceiitral Fissure}^ which is located in the an- terior cerebellar notch. It is between the lingula and lobulus centralis, in the worm; between the fraenulum and ala, in the hemisphere. (2) The Postcentral Fissure}^ in the worm, separates the lobulus centralis from the culmen; and, in the hemisphere, the ala from the anterior crescentic lobule. The fissure fol- lows the anterior border of the superior surface. Both cen- tral fissures terminate on the dorsum of the superior medul- lary lamina. (3) Preclival Fissure. — Behind the culmen and anterior crescentic lobules is the preclival fissure. It bounds the clivus and posterior crescentic lobules in front. It ends at the junc- tion of the anterior and middle thirds of the antero-lateral border in the great horizontal fissure. (4) The PostcUval Fissure is located in the posterior cere- bellar notch, from which it curves outward and forward in the superior surface of the hemispheres. It separates the clival lobe from the folium cacuminis, in the worn!, and the postero- superior lobules in the hemispheres. It ends in the horizontal fissure at the junction of the posterior and middle thirds of the antero-lateral border. (11) Pissurse interlobulares. (12) Sulcus prsecentralis cerebelU. (13) Sulcus postcentralis. HIND-BRAIN. [05 Fissures and lobules of the upper surface of the cerebellum from before backward: Hemisphere. Frsenulum. Ala. Anterior crescentic. Posterior crescentic Postero-superior. Worm. Lingula. Precentral fissure. Lobulus centralis. Postcentral fissure. Culmen. Preclival fissure. Clivus. Post clival fissure. Folium cacuminis. Great horizontal fissure. Hemisphere. Fraenulum. Ala. Anterior crescentic. Posterior crescentic. Postero-superior. Lobes of Superior Surface. — ^These include the divisions of the worm and of the hemispheres, and are five in number. Lingula and Frcenula (Lobus lingulaB). — The lingula^ ^ is a very small lobule of the vermis entirely concealed in the anterior cerebellar notch by the overhanging central lobule. It is a tongue-shaped group of four or five rudimentary trans- verse laminae. It rests upon the superior medullary velum, with which its white center is continuous. Laterally, the lingula tapers off and , is represented, if at all, in the hemi- sphere by a very thin folium called the fraenulum.i^ Thf3 frgenulum is bounded by the superior cerebellar peduncle in front, and by the precentral fissure behind. The pre- central fissure separates the lobp of the lingula from the cen- tral lobe. Central Lohule and Alee (Lobus centralis). — The lobulus centralis is situated between the precentral and postcentral fissures, in the anterior cerebellar notch. It covers the lin- gula and in turn is overhung by the culmen. Four or five (14) Lingrula cerebelll. (15) Vinculum Ungnlse cerebelli. I06 THE BRAIN AND SPINAL CORD. small transverse laminaB make it up. On sagittal section, it is seen to form a single branch of the corpus trapezoides (arbor vitae). The laminae of the central lobule, continuing into either hemisphere, form a triangular or wing-like lobule, the ala (ala lobuli centralis). Oulmen and Anterior Crescentic Lohules (Lobus culminis). — In the culmen^^ the surface of the cerebellum reaches its highest elevation. It is a large lobule and occupies more than half of the upper surface of the worm. It is made up ot three or four prominent laminae, which extend laterally into the hemispheres; and, there, form the anterior cres- centic lobules.i"^ The latter occupy about one-third of the upper surface of the hemispheres. The preclival fissure sepa- rates the culmen and anterior crescentic lobules (the lobe of the culmen) from the clival lobe. Clivus and Posterior Crescentic Lohules (Lobus clivi). — The clivus^ ^ forms the posterior slope, as the culmen forms the summit, of the monticulus cerebelli. The clivus has about half the extent of the culmen. Its laminae are con- tinued into either hemisphere, where they form the large posterior crescentic lobule.^^ The increased size in the hemisphere is due to the expansion of the secondary folia found in the worm. The anterior and posterior crescentic lobules constitute the quadrate lobe,^^ which forms the an- terior two-thirds of the superior surface of the hemisphere. The clivus and its hemispherical extensions are inclosed between the preclival and postclival fissures. The Folium Cacuminis and Postero-superior Lohules (16) Culmen monticull cerebelli. (17) Pars anterior lobuli quadrangularls. (18) Declive monticull cerebelli. (19) Pars posterior lobuli quadrangrularis. (20) Lobus quadrangularis. HIND-BRAIN. 10/ (Lobus cacuminis) lie behind the postclival and in front of the great horizontal fissure. The folium cacuminis^^ is the terminal lamina in the superior worm, and occupies the pos- terior cerebellar notch. It is beset with rudimentary folia, which are largely developed in the hemispheres. The postero- superior lobule^^ is, therefore, very large in comparison with the folium cacuminis. It expands lateralward to the postero- lateral border of the hemisphere, which it forms. It com- prises the posterior third of the hemisphere's superior surface. INFERIOR SURFACE OF THE CEREBELLUM. The inferior surface of the cerebellum^s is prominent laterally and depressed centrally (as the organ is view^ed inverted), the hemispheres being separated by the antero- posterior groove, called the vallecula?"^ The valley is occu- pied by the inferior worm and is bounded on either side by a small fissure, between the worm and the overhanging hemi- sphere, called the sulcus valleculce. The inferior cerebellar surface is limited by the great horizontal fissure and the medullary body of the cerebellum. It is more complex than the superior surface ; and its fissures are more sharply curved forward as they pass from the worm into the hemispheres. Fissures of Lower Surface. — The interlobular fissures of this surface are very deep. They are three in number, namely : (1) The Postnodular Fissure is in the anterior end of the worm between the nodule and uvula. In the hemisphere it winds forward and outward between the inferior medullary velum and the tonsil, and then continues lateralward between (21) Folium vermis. (22) Lobulus semilunaris superior. (23) Facies cerebelli inferior. (24) Vallecula cerebelli. io8 THE BRAIN AND SPINAL CORD. flocculus and digastric lobule to the anterior end of the great horizontal fissure. (2) The Prepyr amidol Fissure, between the uvula and pyramid, is very concave in the hemispheres. It curves out- ward and forward around the tonsil, separating it from the digastric lobule. It terminates behind the flocculus in the postnodular fissure. (3) The Post pyramidal Fissure, between the pyramid and tuber valvulae, is near the posterior end of the worm. It forms an oblique groove in either sulcus valleculas, from which three concentric fissures extend into the hemispheres. The anterior of the three (the pregracile), usually consid- ered the postpyramidal fissure in the hemisphere, separates the digastric lobule from the postero-inferior lobule; the remaining two (midgracile and poetgracile) subdivide the postero-inferior lobule into anterior and posterior slender and inferior semilunar sub-lobules. The last is bounded ]>ehind by the great horizontal fissure. Fissures and lobules of the lower surface of the cerebellum, from before backward : Hemisphere. Flocculus. Tonsil. Digastric lobule. Postero-inferior lobule. Worm. Nodule. Postnodular fissure. Uvula. Prepyramidal fissure. Pyramid. Postpyramidal fissure. Tuber valvulae. Oreat horizontal fissure. Hemisphere. Flocculus. Tonsil. Digastric lobule. Postero-inferior lobule. Lobules of Lower Surface. — ^They are not continuous with one another from the worm to the hemisphere as on the HIND-BRAIN. lOQ upper surface. Excepting the posterior lobules, only a small ridge beneath the sulcus valleculas joins them together. The inferior lobes are four in number. Each is composed of a central and two lateral lobules. The lobule in the worm gives the name to the lobe, Nodulus and Flocculi (Lobus noduli). — The nodule^^ is a small lobule at the anterior end of the inferior worm. It is composed of three or four laminae, which project from the middle of the lower surface of the inferior medullary velum. It comprises a single branch of the arbor vitas. Though larger, it is the counterpart of the lingula on the superior velum. It is bounded by the sulcus valleculae on either side. The inferior medullary velum extends laterally from the nodule, and blends with the middle peduncle of the cere- bellum. In front of the tonsil, a fold of gray matter (peduncle of flocculus) ^^ appears on the velum. That gray matter enlarges more externally to a tufted mass, called the flocculus. The flocculus is separated from the tonsil and digastric lobule by the postnodular fissure. The whole line of structures, namely, the nodule, velum, peduncle and floc- culus, form the lobe of the nodule. Uvula and Tonsils (Lobus uvulae). — ^The uvula^'^ com- prises a considerable part of the vermis inferior behind the nodule. It broadens backward and is widest next the pyra- mid. Bounded on either side by the sulcus valleculae, it projects into the valley like the uvula into the isthmus of the fauces. Three moderate sized laminae and six or eight small folia make up the uvula. A slight ridge, the furrowed hand, joins it to the tonsiPs in the hemisphere. From the furrowed band the tonsil expands downward and backward, forming a lobule of nearly a dozen sagittal laminae. The tonsil (or (25) Nodulus vermis. (27) Uvula vermis. (26) Pedunculus flocculi. (28) Tonsilla cerebelli. no THE BRAIN AND SPINAL CORD. amygdala) overhangs the side of the uvula and conceals the furrowed band, medially; and, behind, it conceals the con- necting ridge between the pyramid and digastric lobule. The fossa containing the tonsil is the bird's nest (nidus avis). Behind the uvular lobe, composed of the above three lobules, are the prepyramidal fissure and the lobe of the pyramid. Pyramid and Digastric Lohules (Lobus pyramidis). — As seen from the surface, three or four distinct laminae make up the pyramid,29 which is the most prominent lobule of the inferior worm. A low connecting ridge joins the pyramid to the digastric lobule in the hemisphere. The digastric (or biventral) lobule^^ is triangular in outline. Its base looks toward the flocculus and is bounded by the postnodular fissure; its apex is continuous with the connecting ridge. The laminae composing it radiate from the apex toward the base, and are divided into two groups by a very deep intra- lobular fissure. The postpyramidal fissure bounds it postero- extemally, and separates it from the postero-inferior lobule. Tuber Valvulce and Postero-inferior Lohules (Lobus tu- beris). — The tuber valvulae^^ forms the posterior end of the inferior worm. It resembles the lobules of the vermis su- perior, because its half dozen tertiary laminae are continued into the hemispheres, the sulcus valleculae not cutting them off. The great horizontal fissure separates it from the folium cacuminis of the superior worm. The postero-inferior lobule^^ comprises the posterior two-thirds of the inferior surface of each hemisphere, extending from the digastric lobule to the postero-lateral border. Twelve to fifteen laminae compose the lobule. They are divided into three groups by the mid- (29) Pyramis vermis. (30) liObulus biventer. (31) Tuber vermis. (32) Lobulus semilunaris inferior. HIND-BRAIN. Ill gracile and postgracile fissures; the groups are named the anterior slender, or pregracile, posterior slender, or post- gracile, and inferior semilunar. The inferior semilunar sub- lobule, only, is continuous with the laminse of the tuber. GRAY MATTER OF THE CEREBELLUM. The gray matter of the cerebellum is composed of cortex which covers the cerebellar laminae and of ganglia imbedded in the medullary center. 1. Cortical Gray Matter. The cortex of the cerebellum (substantia corticalis) is made up of two microscopic layers, viz., (1) a superficial, molecular, or gray cellular layer, and (2) a deep, nuclear, or rust-colored granular layer. (1) Superficial, Molecular, or Gray Cellular Layer. — Thickest on the laminae and thinnest beneath the fissures, this layer contains small spheroidal, or stellate, cell-bodies with their processes, and large flask-like cell-bodies with their dendrites and axoijes (the cells of Purkinje) and a close network of fibers. Cells. — The bodies of Purhitijes cells are located near the deep surface of the cellular layer (stratum gangliosum). Bach has one axone which, after piercing the granular layer, becomes a fiber of the medullary center (a projection fiber). From the outer end of each cell-body antler-like processes, the dendrites, are given off; they rajnify toward the surface in a plane at right angles to the intralobular fissures. The spheroidal cell-bodies form an outer and inner layer. They have rich dendritic processes and one axis-cylinder each. The dendrites ramify throughout the cellular layer. In the outer layer the stellate cell-bodies are smaller than in the inner 112 THE BRAIN AND SPINAL CORD. layer. Their axis-cylinders run parallel with the surface and at right angles to the intralobular fissures. They branch freely and terminate in a manner unknown. The inner layer contains the 'T)asket cells." Their axis-cylinder processes run parallel with the former, and give off vertical branches which descend to Purkinje's corpuscles and inclose them in a basket-work of filaments. Fibers of the gray cellular layer have three sources: (a) The dendritic and axonic processes of neurones within the layer; (b) the processes of cell-bodies in the granular layer. The latter comprise, first, the neurogliar fibers of Bergmann (vertical), which extend from the granular layer outward to the surface of the lamina, where they form a feltwork like the limiting membranes of the retinas; and, second, the axones of the cell-bodies in the granular layer, whose T-branches run parallel with the interlobular fissures in the superficial layer, (c) The fibers of the medullary center' (projection fibers) rise or end largely in the cellular layer. The axones of Purkinje's neurones compose most of the cen- trifugal projection fibers. The centripetal fibers, which rise either in other parts of the brain or in the spinal cord and ganglia, terminate in end-tufts or moss-like appendages (Cajal) chiefly in the superficial layer. (2) The Deep, Nuclear, or Rust-colored Granular Layer is of uniform thickness. It blends centrally with the medul- lary body. Cells of the Granular Layer. — The granules are small round, or stellate cell-bodies, largest near Purkinje's cells, closely packed externally, but scattered among the projection fibers centrally. Each granule has one axone. It runs out into the cellular layer, branches T-like, and forms many of the tangential fibers of that layer. Dendritic processes are HIND-BRAIN. II3 abundant. They ramify chiefly within the granular layer. The neurogliar cell-bodies, which originate the vertical fibers of Bergniann, lie near the cells of Purkinje (N. 8, Add.). Among the fibers of the granular layer are included the processes of the granules and glia cell-bodies, and the effer- ent and afferent projection fibers. The functions of the stellate cells, the ^'basket cells'^ and the granule cells are probably receptive and associative; they receive impulses through the centripetal projection fibers and transfer those impulses to the dendrites or bodies of Pur- kinje's cells. Purkinje's cells originate impulses for the co- ordination of muscular action (Gordinier), and for the inhi- bition of nervous activity in the opposite cerebral hemisphere (Eussell). Hence lesions in the cerebellum produce inco- ordination, irritability and, rarely, convulsions. II. Ganglionar Gray Matter. The ganglia of the cerebellum are the corpus dentatum and the three nuclei of Stilling. The Corpus Dentatum^ is a wavy, sinuous pouch of yellow- ish-brown gray matter imbedded in the medullary body of each hemisphere. It is filled with white fibers, which issue from its anterior, open end^ and form the greater part of the superior cerebellar peduncle. Stellate cell-bodies (from 6 microns to 40 microns in diameter) are the essential element of both the corpus dentatum and Stilling's nuclei. Nuclei of Stilling. — One of these, a club-shaped mass, the cork-like nucleus emboliformis, partly closes thfe hilus of the dentate body. Medial to that is an elongated antero-posterior ganglion, bulbous behind, called the nucleus glohosu^. The third nucleus is in the anterior end of the worm, just above (1) Nucleus dentatus. (2) Hilus nuclei dentati. 114 THE BRAIN AND SPINAL CORD. the fastigium of the fourth ventricle. It is called the nucleus of the highest point of the roof, nucleus fastigii. In the two last the stellate cell-bodies are larger than in the nucleus emboliformis or corpus dentatum; but, otherwise, they are alike in structure. The nucleus fastigii and nucleus globosus form the terminal station for the acustico-cerebellar tract, which tract sends collaterals to the nucleus emboliformis and corpus dentatum. In this manner these nuclei are associated with the vestibular nuclei (auditory) of the opposite side. V7HITE MATTER OF THE CEREBELLUM. The white matter of the cerebellum is arranged in three systems similar to that of the cerebrum: I. Projection, or peduncular, fibers. II. Commissural fibers. III. Association fibers. I. Projection Fibers. These include all fibers of the medullary body^ as it issues from the anterior cerebellar notch. The fibers are in con- tinuity with the branches of the medullary body* and together constitute the arbor vitce. Dividing medially into a superior and an inferior lamina (united laterally), the medullary body forms the tent^ and lateral recesses^ of the fourth ven- tricle. The inferior lamina is the inferior medullary velum,'' whose fibers pass into the nodule and fiocculi. The superior lamina forms the superior medullary velum and three pairs of cerebellar peduncles. Superior Peduncles. — Two bundles of fibers maJ^e up the (3) Corpus medullare. ,. • (4) Laminae medullare s. • (5) Fastigium. (6) Recessus lateralis ventriculi quarti. (7) Velum medullare posterius. HIND BRAIN. Ilg superior peduncles.^ They are afferent and efferent. First, the fibers to the cerebrum which are axones of cell-bodies situated chiefly in the corpus dentatum, but which axe com- bined with a few axones of Purkinje's cells. This group of fibers ends chiefly in the opposite red nucleus, where the second group rises. The second group, rising in the opposite red nucleus, ends in the corpus dentatum. The greater num- ber of fibers in the superior peduncles decussate in the teg- mentum. The superior medullary velum^ arches over the fourth ventricle between the superior peduncles. It is com- posed chiefly of longitudinal fibers running between the worm and the cerebrum. One distinct bundle, derived from the spinal cord, passes through it to the worm. It is the antero- lateral ascending cerebellar tract (Hoche). The decussating root-fibers of the fourth nerve (trochlear) course transversely through the superior velum, also certain commissural fibers of the hind-brain. Middle Peduncles. — They pass to the pons and form its ventral and middle transverse fibers. They also are both afferent and efferent. The fibers of the middle peduncle^ ^ rise, first, from every part of the cerebellar cortex. They cross one another in the peduncle, fibers from the anterior part of the hemisphere running to the posterior portion of the pons, and vice versa. Passing toward the median iine, the fibers end in the nuclei pontis and nuclei of the formatio reticularis on both sides of the raphe. Second, the remain- ing fibers are axones of cell-bodies situated mainly in the opposite nucleus pontis. The latter form a segment in the indirect motor paths contained, above the pons, in the medial and lateral fifths and the intermediate bundle of the crusta (8) Brachia conjunctiva. (9) Velum medullare anterlus. (10) Brachium pontis. Il6 THE BRAIN AND SPINAL CORD. Collaterals from both groups of fibers ascend and descend in the pons. They run upward with both crusts, but chiefly with the opposite one; and they accompany the fillet and posterior longitudinal bundle of the same side to the nuclei of the third, fourth and sixth cranial nerves. The Inferior Peduncles can be traced to the upper part of the hemispheres and to the worm. Inferiorly, they become the restiform bodies^ ^ of the medulla oblongata. The bun- dles of component fibers are very numerous : ( 1 ) The direct cerebellar tract, whose origin is in Clark's column of the cord and termination in the superior worm. (2) The ex- ternal arciform fibers of the medulla (posterior and anterior), which rise in the nucleus gracilis and nucleus cuneatus and end in the vermis superior, the former on the same and the latter on the opposite side. (3) The acustico-cerebellar tract from the nuclei of the vestibular nerve to the opposite nucleus fastigii and nucleus globosus. (4) A bundle from the lateral nucleus of the medulla to the cerebellar cortex on the same side. (5) The antero-lateral, descending cerebellar tract, which runs from the cortex of the cerebellum to the anterior gray horn in the cord. (6) The internal arciform fibers to the opposite lower olive, the cerebello-olivary tract. Most of the fibers which leave the cerebellum by way of the middle and inferior peduncles are axones of Purkinje's cells; they connect the cerebellum with the motor nuclei of cranial and spinal nerves. II. Commissural Fibers. The cerebellar hemispheres are joined by transverse fibers, of which there are two sets, namely: One near the anterior end of the worm beneath the central lobe, and the other at the posterior end of the worm. (11) Corpus restifarme (singr.). HIND-BRAIN. II7 III. Association Fibers. Antero-posterior fibers join the cerebellar laminae to one another. They arch beneath the fissures, and remain in one hemisphere. BLOOD SUPPLY OF CEREBELLUM. Three pairs of arteries supply the cerebellum. The supe- rior cerebellar, from the basilar, supplies all the superior surface except a narrow zone at the posterior border; and the anterior inferior cerebellar, also from the basilar, and the posterior inferior cerebellar, from the vertebral, supply the inferior surface and the posterior part of the superior surface. The superior cerebellar artery, rising from the basilar just behind the posterior cerebral, from which it is separated by the oculomotor nerve, winds dorsally around the mid-brain and distributes branches to the geniculate bodies, corpora quadrigemina, velum interpositum and dorsal surface of the pons, besides the vermis superior cerebelli and nearly all the superior surface of the hemisphere. It anastamoses with both the inferior cerebellar arteries. The anterior inferior cerebellar is given off by the basilar near its origin. It runs lateral ward, behind the flocculus, keeping close to the anterior border of the hemisphere. In its course it passes anterior to the abducent nerve and posterior to the facial and auditory nerves. The posterior inferior cerebellar artery is the largest branch of the vertebral and is given off just before the verte- bral arteries unite and form the basilar. Passing first between the root-bundles of the hypoglossal nerve and then between those of the spinal accessory and vagus nerves, the posterior inferior cerebellar artery bends at a right angle backward and runs between the medulla and the cerebellar hemisphere where it divides into an internal and an external Il8 THE BRAIN AND SPINAL CORD. branch. The Internal branch follows the sulcus valleculae and gives branches to the medial part of the hemisphere and the vermis inferior. It anastamoses with its fellow of the opposite side. The External branch runs lateralward from the posterior cerebellar notch over the inferior surface of the hemisphere; its terminal branches wind around the postero- lateral border and communicate with the superior cerebellar artery on the upper surface of the hemisphere. The un- divided trunk of the posterior inferior cerebellar artery gives small branches to the medulla oblongata and supplies the choroid tela of the fourth ventricle. Three sets of veins carry the blood away. The superior cerebellar veins pour their blood against the current into the straight sinus. The inferior cerebellar veins empty in like manned into the lateral sinus; and the lateral cerebellar veins, into the superior petrosal sinus. The trunks of both veins and arteries ramify in the pia mater. Lymphatics. — There are no lymphatic vessels in the cere- bellum, but the perivascular lymph spaces carry out the lymph and pour it chiefly into the subarachnoid space. Section II. The Pons Varolii. The pons is the ventral part of the hind-brain, the cere- bellum being its dorsal portion. The pons is develpped from the floor of the epencephalon. It is so named because it forms the connecting link, or bridge, between the mid-brain, above, and the cerebellum and medulla oblongata, below; between the medulla and cerebellum, and between the two cerebellar hemispheres. In shape the pons is roughly cylindrical. A coronal section of it resembles an inverted transverse section of the penis. HIND-BRAIN. II9 It has a broad basal or ventral part^^ ^j^j ^ narrow dorsal portion.^ 3 Size. — The pons is about one inch long. It is a little broader than long, and measures an inch, dorso-ventrally. Position. — It rests in the anterior end of the groove which extends from the foramen magnum to the dorsum sellae, and lies between and ventral to the hemispheres of the cerebellum. Superiorly, it joins the mid-brain; and, behind, it is con- tinuous with the medulla oblongata. Surfaces of the Pons. — The pons has four surfaces, viz., superior (attached) ; inferior (attached) ; ventral (free), and dorsal (free) ; and two borders, namely, right and left lateral, continuous with the middle peduncles of the cere- bellum. i* The Superior and Inferior Surfaces are made by section, and are directly continuous with the mid-brain above and the medulla below. Ventral Surface (Tuber annulare). — The ventral surface of the pons looks downward and forward, and rests on the sphenoid bone behind the sella Turcica. It is divided into lateral halves by the sulcus basilaris, containing the basilar artery. Antero-posteriorly, the surface is slightly convex, and is markedly so from side to side. It shows transverse striations, which converge laterally, due to the fibers that form it, and enter the middle peduncles of the cerebellum. The fibers of the tuber annulare are not exactly transverse in direction. Those at the anterior end of the pons are arched, convex forward, and form a rounded margin, which covers the lower part of the crustae of the mid-brain; at the pos- terior extremity of the pons, the fibers are convex backward (12) Pars basilaris pontis. (14) Brachia pontis. (13) Pars dorsalis pontis. 120 THE BRAIN AND SPINAL CORD. and pfirtially conceal the pyramids of the medulla oblongata. The two roots of the 5th nerve (trifacial) ^^ issue from the lateral border (Henle) of this surface, a little in front of the middle. The Dorsal Surface of the pons is concealed by the cere- bellum. Medial Portion. — It presents a median longitudinal elevation due chiefly to the superior peduncles of the cere- bellum^^ and valve of Yieussens}'^ The peduncles converge forward and upward and run beneath the inferior quadri- geminal bodies of the mid-brain. The valve spans the in- terval between the peduncles and forms the floor of the slight groove which separates them. A low and narrow ridge runs from the corpora quadrigemina down the middle of the valve. It is called the frenulum. In the superior medullary velum (or valve of Vieussens), the 4th cranial nerve (n. trochlearis) decussates and issues from its lateral portion on each side of the frenulum. Lateral Portion. — Each lateral portion of the dorsal sur- face is depressed. On this depressed portion, the lateral fillet^^ produces a low ridge which, trending upward and toward the median line, winds over the anterior end of the superior peduncle and terminates at the inferior corpus quad- rigeminum. This ridge is joined by a much slighter one, which runs from the valve outward and forward over the posterior end of the superior peduncle; it is caused by a bundle of fibers from the antero-lateral ascending cerebellar tract. WHITE MATTER OF THE PONS. The pons is composed of transverse and longitudinal white fibers and of gray matter. The transverse fibers are found in (15) Nervus trig-eminus. (17) Velum meduHare anterius (16) Brachia conjunctiva. (18) Lemniscus lateralis. HIND-BRAIN. 121 the ventral portioni^ of the pons; the longitudinal, in the dorsal part,^^ and also intersecting the middle transverse fibers. TRANSVERSE FIBERS OF PONS. The transverse fibers form three consecutive layers in the ventral area of the pons, viz., the ventral, the middle, and the dorsal layer. They lie one upon another. The Ventral Transverse Fibers (superficial transverse) 21 form a thin layer constituting the tuber annulare, or ventral surface of the pons. Middle Transverse Fibers (ventral deep-transverse). — These form a thick lamina dorsal to the ventral transverse fibers and in contact with the ventral lamina. They are intermingled with longitudinal fibers running from the crustae (middle three-fifths) down to the pyramids of the medulla oblongata and with fibers of the fronto-pontal, inter- mediate and temporo-pontal tracts which end in the pons. In the meshes between the intersecting fibers are masses of gray matter called the nuclei pontis. The middle and ventral transverse fibers form the middle cerebellar peduncles.22 They are made up (1) of axones of Purkinje^s cells which end in the nuclei pontis and nuclei of the formatio reticu- laris on both sides of the pons, and (2) of axones of cell- bodies in these same nuclei, especially the nuclei pontis, which terminate in the cerebellar cortex of the opposite side; The Dorsal Transverse Fibers (dorsal deep-transverse) com- pose a thin layer on the dorsum of the middle transverse and pyramidal fibers, separating them from the formatio reticu- laris. The dorsal transverse lamina is best marked in the posterior part of the pons, where it is called the trapezium. (19) Pars basilaris pontis. (21) Fibrse pontis superflciales. (20) Pars dorsalis pontis. (22) Brachia pontis. 122 THE BRAIN AND SPINAL CORD. The trapezium forms the boundary between the dorsal and ventral areas of the pons. It rises chiefly from the nuclei of the cochlear nerve and, after decussating in the raphe, is continued up in the lateral fillet to the corpus quadrigeminum inferius. A few fibers join the tract directly from the cochlear nerve. The nuclei of the trapezium, of superior olive and of lateral fillet form way-stations for a number of its fibers. The trapezium and lateral fillet form the second stage in the auditory conduction path, the auditory im- pulses having reached the trapezium and lateral fillet through the auditory nerve are continued (a) through the brachium inferius and (b) the acustic radiations to the temporal cortex. LONGITUDINAL FIBERS OF PONS. Like the transverse, the longitudinal fibers of the pons are arranged in three distinct laminae, viz., the ventral, the middle and the dorsal. The last two are in contact with one an- other in the dorsal area^s of the pons ; but the ventral lamina is separated from the middle by the trapezium. The Ventral Longitudinal Fibers (ventral deep-longitu- dinal) are the motor fibers of the crustae. The pyramidal fibers^* run from the middle three-fifths of each crusta down through the middle transverse layer of the pons to the pyra- mids of the medulla oblongata. They form a thick bundle en either side of the median line, which presses down the ventral transverse fibers and produces the sulcus basilaris. The ventral longitudinal fibers are to a small extent made up of fibers, probably collaterals, from the middle cerebellar peduncles (chiefly from the opposite one) which run both toward the cerebrum and the spinal cord. The nuclei pontis, one on either side, are situated among them. The pyramidal (23) Pars doi:salis pontis. (24) Fasciculi lon|ritudinales pontis (pyramidales). HIND-BRAIN. I23 tracts diminish in size during their descent, because of the fibers which leave them to decussate and end in the nuclei of motor cranial nerves. Middle Longitudinal Fibers (dorsal deep-longitudinal). — These are contained in the formatio reticularis. They are dorsal to the trapezium, and lie in the floor of the fourth ventricle. Laterally, the middle lamina is in contact with the dorsal longitudinal layer, the superior peduncles of the cerebellum lying directly on it; but, medially, the two laminae are separated from one another by the fourth ven- tricle. The middle longitudinal fibers are mingled with many oblique fibers ; and, thus, there is produced the net-like arrangement suggesting the name, formatio reticularis. The formatio reticularis of the pons is continued in the medulla oblongata. Considerable gray matter is found in the meshes, especially in the part next the fourth ventricle. The latter contains the nuclei of the fifth, sixth and seventh cranial nerves and a part of the nucleus of the eighth nerve. The remaining gray matter constitutes the nuclei of the formatio reticularis, etc. In the formatio reticularis are contained six distinct bundles of longitudinal fibers: The fillet, the ante- rior and the posterior longitudinal bundle, the olivary bundle, the crossed descending tract from the red nucleus, and in the lower part of the pons the ascending root of the trifacial nerve. According to Hoche, also, the antero-lateral ascend- ing cerebellar tract (N. 9, Add.). (1) The Fillet^^ Fibers form a broad flat bundle next the trapezium. The width of the bundle is almost equal to half the transverse axis of the pons; the lateral fillet lies just beneath the dorsal surface, and the medial runs along the raphe. Anterior to the pons we have the medial, superior (25) Lemniscus— L. Lateralis, L. Medialis, L. Superior. 124 THE BRAIN AND SPINAL CORD. and lateral fillets, which have been traced through the teg- mentum of the mid-brain to the optic thalamus and the superior and inferior quadrigeminal bodies. (2) Posterior Longitudinal Bundle?^ — It is a small fas- ciculus situated near the raphe^, and just beneath the gray matter in the floor of the fourth ventricle. It is continued down into the anterior column of the spinal cord without decussation. Both ascending and descending fibers are found in it. Its longest ascending fibers rise in the anterior cornu of gray matter in the spinal cord. Fibers are added to it from the sensory nuclei of cranial nerves, and from the cerebellum by way of the middle peduncles. Along its course fibers leave it and end in the motor nuclei of cranial nerves, especially the third and fourth. The bundle ends in the hypothalamic region. Many of its fibers decussate through the raphe in the medulla, pons and mid-brain ; the remainder cross through the posterior commissure. Motor fibers run through the posterior longitudinal bundle from the nucleus of the sixth to the third nerve and from the motor oculi to the facial nerve. (3) TJie Anterior Longitudinal Bundle^'^ descends from, the superior quadrigeminal body ventral to the posterior longitudinal fasciculus, through the mid-brain, pons and medulla; and, in the cord, it runs along the apex of the anterior cornu of gray matter, in which it terminates, chiefly in the cervical region. It is the pupillo-dilator tract. (4) The Olivary Bundle^^ is an ascending tract. It be- gins at the dorsal surface of the inferior olive, from which it probably rises. It ascends through the formatio reticularis of the medulla, pons and mid-brain, and, according to Flech- (26) Fasciculus longitudinalis medialis. (27) Fasciculus ventralls. (28) Fasciculus tegmenti centralis. HIND-BRAIN. I25 sig, ends in the globus pallidns of the lenticular nucleus, though certain fibers may continue through the lenticular loop, without interruption, to the cortex. The olivary bundle is probably the second stage in the afferent tract of which the triangiilar tract of Helwig is the first stage. In the posterior part of the pons, the olivary bundle lies on the lateral part of the trapezium, between it and the fillet. Higher up it is in the center of the formatio reticularis, hence its synonym, central tegmental tract. (5) Crossed Descending Tract of the Red Nucleus. — It is found in the pons among the medial fibers of the lateral fillet. It runs from the red nucleus through the raphe, in the upper part of the mid-brain; and, from there, descends to the lumbar region of the spinal cord (Barker). Its fibers gradually disappear in the lateral horn and center of the crescent of gray matter (see Mid-Brain, p. 65). (6) Ascending Boot of the Trifacial or Fifth Nerve (in- ferior sensory root) .^^ — ^In the lower half of the pons is seen a small bundle of fibers which begins near the tubercle of Eolando in the medulla oblongata. It runs forward close to the lateral part of the floor of the fourth ventricle and joins the superior sensory root ventral to the superior cerebellar peduncle. The Dorsal Longitudinal Fibers (superficial longitudinal) form the medial portion of the dorsal surface of the pons. They bound laterally and form the roof of the superior half of the fourth ventricle. The dorsal longitudinal fibers com- pose the superior peduncles of the cerebellum and the valve of Vieussens. The peduncles rest on the formatio reticu- laris. Between them the valve arches over the fourth ven- tricle (see Cerebellum, pages 102, 114). (29) Tractus spinalis nervi trigemini. 126 THE BRAIN AND SPINAL CORD. GRAY MATTER OF THE PONS. In the pons gray matter is found in two situations: (1) In the interstices between the middle transverse and ventral longitudinal fibers, the nuclei pontis; and (2) in the for- matio reticularis, the floor of the fourth ventricle. The nuclei pontis are masses of gray matter, on either side the raphe, containing the bodies of multipolar nerve cells. They receive many fibers from the middle peduncles of the cerebellum and each contributes many to the opposite pe- duncle. The nucleus pontis of each side receives the ter- minals of the descending tracts which form the inner and outer fifths of the crusta and the intermediate bundle of the same, and thus connects these tracts with the cerebellum. The gray matter of the formatio reticularis includes the fc^uperior olive; the nuclei of the trapezium; the nuclei of the formatio reticularis; and the nuclei of the fifth, sixth and seventh cranial nerves, and a part of the dorsal nucleus of the auditory nerve. The nerve nuclei will be further noticed in the description of the fourth ventricle. Superior Olivary Nucleus. ^^ — It is situated in the lateral part of the formatio reticularis in the dorsal portion of the trapezium. It contains small bodied nerve cells; and, in this respect, resembles the oKve of the medulla. In size it is microscopic. The superior olive constitutes a subordinate relay in the auditory path, receiving fibers from the cochlear nuclei of both sides and contributing fibers to both lateral fille^riS, In their course to the fillets, fibers of the auditory path form the trapezium (N. 10, Add.). Nuclei of the Formatio Reticularis. — These nuclei are scattered in the reticular formation from the medulla to the superio quadrigeminal bodies. They contain the bodies of (30) Nucleus olivaris superior. HIND-BRAIN. I27 large multipolar cells, hence the name adopted by Koelliker, Nucleus magnocellularis diffusus. The nuclei are interposed in the frequently interrupted tracts of the reticular forma- tion. Their neurones, which are both ascending and de- scending in conduction, send their axones toward the raphe, where they cross to the opposite side. Axones of Purkinje's cells and collaterals from the nuclei of cranial nerves ter- minate in relation with them. Lesions in the pons are usually attended by crossed paraly- sis. The paralysis and anesthesia of parts supplied by spinal and by bulbar cranial nerves are on the opposite side, but the fifth, sixth and seventh cranial nerves of the same side as the lesion are apt to be involved. Conjugate deviation occurs when the nucleus of the sixth nerve is affected; and strabismus when the root fibers, but not the nucleus, are involved. The strabismus is external if the lesion be irrita- tive and internal if the root fibers are destroyed. Destructive lesion in the nucleus of the seventh nerve causes inferior paralysis of the face, the frontalis, pjrramidalis nasi, corru- gator supercilii and orbicularis palpebrarum not being affected. Complete facial paralysis occurs if the root-fibers of the facial nerve be destroyed in the genu or beyond it. BLOOD SUPPLY OF PONS. The vertebral, basilar, posterior cerebral and superior cere- bellar arteries supply the pons. The short and transverse branches of the basilar artery furnish the greater portion of blood to the ventral area of the pons, while the superior cerebellar artery supplies the valve of Yieussens^^ and the superior cerebellar peduncles.^^ The branches enter the median raphe, also the substance of the pons elsewhere, es- pecially along the nerve roots, and run at right angles to the surface into it. (31) Velum medullare anterius. (32) Brachia conjunctiva. CHAPTER VI. THE AFTER-BRAIN, OR MEDULLA OBLONGATA. Situation. — The medulla oblongata is the distal, or caudal, part of the brain. It may be regarded as the expanded intra- cranial portion of the spinal cord, hence the synonym, spinal huTb. It occupies the basilar groove of the occipital bone, posterior to the pons; and is continuous with the spinal cord through the foramen magnum. Dorsally, it is in part con- cealed in the valley of the cerebellum. The vertebral arteries wind forward around it, and form the basilar at its junction with the pons. Size. — The medulla is about an inch long, and dorso- ventrally, is a half-inch thick. Its width at the lower end is a half-inch, also. At the upper extremity it measures from three-quarters of an inch to one inch in width. Its shape resembles an inverted frustum of a cone flattened dorso-ventrally at the base. The truncated apex of the frustum, which is nearly circular in outline, is continuous with the spinal cord; and the flattened base joins the pons Varolii. On the ventral surface, a transverse groove marks the boundary between the medulla and pons. The medulla oblongata is a bilateral organ composed of symmetrical halves. In the interior, the two halves are united by both gray and white matter in the raphe, but on the surface they are partially separated by the anterior and the posterior median fissure.^ These fissures are continuations of the same (1) Fissura mediana anterior, posterior. THE AFTER-BRAIN. I29 in the spinal cord, but neither extends the whole length of the medulla. The anterior median fissure is interrupted in the lower part of the medulla by the crossing of two large tracts of fibers, forming the decussation of the pyramids; while only through the lower half of the medulla does the posterior median fissure extend. Origin. — The medulla oblongata is developed from the metencephalon (myelencephalon) of the embryo. The met- encephalic floor and walls thicken and form the greater part of the medulla. Infer iorly, the roof undergoes some thick- ening; but it stretches out into a single layer of epithelium, superiorly, which is continuous at its upper end with the inferior medullary velum of the cerebellum. Ventricle. — The common cavity of the fourth and fifth brain vesicles persists in the mature brain as the fourth ven- tricle. The fourth is, therefore, the ventricle of the adult hind-brain and after-brain. SURFACES. The Medulla Oblongata presents four surfaces: The ven- tral, dorsal and two lateral, separated by the vehtro-lateral and dorso-lateral grooves. In the upper medulla, the sur- faces are clearly defined; but they become less distinct as they descend to the posterior and nearly circular extremity. The Y entro-lateral Groove^ separates the ventral from the lateral surface, and is in line with the exits of the anterior roots of the spinal nerves. No corresponding groove exists in the cord. From the ventro-lateral groove issue the roots of the hypoglossal nerve. The abducent (or sixth) nerve rises in line with it from the transverse groove between the pons and the medulla. Dorso-lateral Groove. — The posterolateral fissure of the (2) Sulcus lateralis anterior. 130 THE BRAIN AND SPINAL CORD. spinal cord, continued into the medulla, becomes the dorso- lateral groove.^ Through the fissure in the cord, pass the posterior roots of the spinal nerves; from the groove in the medulla, rise the accessoiy root of the eleventh and the roots of the tenth and ninth cranial nerves. The seventh and eighth cranial nerves rise together at the anterior end of the groove. The last two come out between the medulla and pons. The dorso-lateral groove is not parallel with the axis of the medulla, but bends outward and forward as it ascends. Inferiorly, it is obliterated for a short distance by the crossing of the direct cerebellar tract from the lateral to the posterior surface. This groove separates the lateral from the dorsal surface. The Ventral Surface* of the medulla, bounded on either side by the ventro-lateral groove, extends from the transverse sulcus behind the pons down to the spinal cord. It is made up of symmetrical halves united, below, by the decussation of the crossed pyramidal tracts; but separated, above, by the anterior median fissure, which terminates at the posterior end of the pons in a blind foramen (foramen caecum of Vicq d'Azyr). On either side of the median fissure, the ventral surface presents a fusiform eminence, most prominent near the pons, called the pyramid. Two tracts of longitudinal fibers form the pyramid, viz. : The crossed pyramidal tract, next the anterior median fissure; and the uncrossed (direct) pyramidal tract, which runs next the ventro-lateral groove. Transverse fibers are also seen crossing the pyramid from within outwaj-d. A small bundle runs near^the pons, called the ponticulus of Arnold; and a more or less continuous sheet of fibers, the anterior external arciform fibers, emerges from the anterior median fissure and winds around the me- (3) Sulcus lateralis posterior. (4) Facies anterior. THE AFTER-BRAIN. I3I dulla to the dorsal surface, where its fibers enter the restiform body. The ventral surface is identical with the surface of the two anterior areas of the medulla. Lateral Surface. — There are a right and a left lateral surface.^ Each is bounded by the ventrolateral and the dorso-lateral grooves; and is inclosed between the roots of the hypoglossal nerve, ventrally, and those of the ninth, tenth and the accessory portion of the eleventh, dorsally. Lateral surface is synonymous with surface of the lateral area. The lateral surface is formed above by the olivary hody,^ below, by the lateral tract; and winding backward over both, the anterior external arciform fibers. The Olivary Body is an elongated eminence, a half-inch in length, situated just behind the pons. It is produced by the olivary nucleus in the lateral area of the medulla; and, superficially, is composed of fibers from the antero-lateral ground bundle of the lateral tract. Lateral Tract? — It is made up of three great bundles of fibers : The antero-latei'al ground bundle,^ which, splitting into a superficial and a deep lamina, incloses the olivary nucleus; the antero-lateral descending cerebellar tract,^ run- ning down the ventro-lateral groove; and the antero-lateral ascending cerebellar tract p which runs up the dorso-lateral groove. At the junction of the medulla with the spinal cord the direct cerebellar tract passes from the lateral to the dorsal surface. The anterior external arciform fibers}^ running from the ventral surface backward to the restiform body, may (5) Fades lateralis. (6) Oliva. (7) Funiculus lateralis. (8) Fasciculus proprius antero-lateralis. (9) Fasciculus antero-lateralis superficialis (descendens and as- cendens). (10) Fibrse arcuatse extemse. 132 THE BRAIN AND SPINAL CORD. be SO numerous as to conceal the lateral tract and lower part, of the olive. ' The Dorsal Surface of the medulla^^ comprises all the sur- face inclosed between the diverg-ing dorso-lateral grooves. It embraces the surfaces of the two posterior areas of the medulla. Inferiorly, it is divided into lateral halves by the posterior median fissure/ ^ an^d presents four bundles of fibers in each half. From the fissure outward they are as follows: The fasciculus gracilis, fasciculus cuneatus, fasciculus of Eolando, and the direct cerebellar tract. The fasciculus gracilis is a continuation of the postero- median column of the spinal cord, and the fasciculus cunsor tus and fasciculus of Rolando are in direct continuity with the postero-Iateral column of the cord. These three bundles leave the surface and end in the gracile, cuneate and Rolandic nuclei of the medulla. The direct cerebellar tract is con- tinued up from the lateral column of the spinal cord. Ke- maining on the surface, it runs up to the cerebellum through the restiform body. Superiorly, the dorsal surface, on either side, is formed by a large rounded band of fibers, the restiform hody}^ Of the superficial fibers in the medulla, the direct cerebellar tract, the antero-lateral descending cerebellar tract and the anterior and posterior external arciform fibers are con- tinued into the restiform body; and, as we have already learned, the restiform body contains, in addition to the above three tracts, the acustico-cerebellar tract, the tract from the lateral nucleus and the cerebello-olivary tract. It is also called the inferior peduncle of the cerebellum. A single layer of flattened epithelial cells stretches between the two restiform bodies, and roofs over the posterior part of the (11) Facies posterior. (13) Corpus restiforme. (12) Fissura mediana posterior. THE AFTER-BRAIN. I33 fourth ventricle. It is the roof epithelium. By it the dorsal surface is completed. The Roof Epithelium, seen in the mid-dorsal surface of the medulla, is of triangular shape; its base is attached to the inferior medullary velum of the cerebellum; its apex, which is directed downward, covers the inferior angle of the fourth ventricle; and, laterally, it is attached to the clava, the. cuneate tubercle and the restiform body. The line of at- tachment to the restiform body runs, first, obliquely upward and outward; and then, transversely outward, inferior to the lateral recess. The borders of the epithelium become thick- ened by the addition of neuroglia, and are in continuity with, the ependyma of the ventricle. The thickened apex of the epithelial lamina is called the obex. With the pia mater investing • it, termed the inferior choroid tela}'^ this roof epitheliuni is perforated in the median line near its apex by a foramen, the foramen of Magendie,^^ and over each kteral recess by the foramen of Key and Eetzius.^^ These foramina establish communication between the subarach- noid space and the ventricle. On either side of the median line, a longitudinal invagination of the epithelial lamina dips into the ventricle and is occupied by a vascular fold of pia mater. The latter constitutes the choroid plexus^'^ of the fourth ventricle. If the roof epithelium be torn away, as it usually is with the pia, a rough line of separation is seen winding over the restiform body. That line is the ligula. Two layers of ependyma form it. -^^^T" WHITE MATTER OF MEDULLA. The medulla is made up of white and gray matter, which together bound ventrally and laterally the inferior part of (14) Tela choroidea ventriculi quarti. (15) Apertura mediana ventriculi quarti. (16) Aperturse laterales ventriculi quarti. (17) Plexus choraid^us ventriculi quarti. 134 THE BRAIN AND SPINAL CORD. the fourth ventricle and surround the upper extremity of the sixth ventricle. For the most part the white matter of the medulla is con- tinuous with the longitudinal fibers of the pons and spinal cord, above and below, respectively ; and with the inferior peduncles of the cerebellum, dorso-laterally. To these add the bulbar roots of the eighth to the twelfth cranial nerves to complete the list. Formatio Reticularis. — Superficially, the white matter is collected into great bundles of fibers, such as the pyramids, lateral tracts and restiform body; but, in the deep parts of the medulla, the white matter enters into a great network called the formatio reticularis, which has gray matter in its meshes and embraces all the medulla between the ventricular gray matter, dor sally, and the pyramid, olivary nucleus, and restiform body, ventro-laterally. The formatio reticularis contains many scattered fibers, processes of its intrinsic neu- rones, which form a frequently interrupted and, for the most part, a crossed ascending and descending tract. It is con- tinuous, above, with the reticular formation of the pons, and, below, with the ground bundles of the spinal cord. It con- tains several distinct fasciculi of longitudinal fibers of which the following are the best understood : The posterior and an- terior longitudinal bundles and the descending crossed tract of the red nucleus, which run throughout the medulla and are continued in the cord; and, in the upper part of the medulla, the interolivary fillet (medial and superior), the olivary bundle and the inferior, or spinal, root of the fifth cranial nerve. Transverse and oblique fibers are, likewise, numerous in the reticular formation. They are the internal arciform fibers. In the formatio reticularis is much gray matter which may be considered as the disintegrated H- shaped column continued up from the spinal cord. THE AFTER-BRAIN. 135 Raphe. — Fibers form only a part of the raphe which unites the lateral halves of the medulla. The raphe is, primarily, a sagittal lamina of neuroglia containing the bodies of nerve- cells and decussating, dorso- ventral and longitudinal fibers: (a) The decussating fibers are chiefly the internal arciform. A few are commissural fibers between the nuclei of the pos- terior five cranial nerves, (b) Issuing from the anterior median fissure, the dorso-ventral fibers become the anterior external arciform fibers. Traced dorsally, some of them are found continuous with the acustic striae in the floor of the fourth ventricle, while the greater number rise from the opposite nuclei gracilis et cuneatiis. (c) The origin and destination of the longitudinal fibers are unknown. The white matter of the medulla is divided by the direction of its fibers into three classes or systems : ( 1 ) Transverse fibers; (2) Dorso-ventral fibers; and (3) Longitudinal fibers. (1) The Transverse Fibers of the medulla are chiefly the external and internal arciform fibers.^^ The anterior exter- fial arciform fihers^^ rise in the nucleus gracilis and nucleus cuneatus of the opposite side, decussate in the raphe and issue from the anterior median fissure and ventral surface of the medulla, whence they have been traced over the surface to the restiform body. Perhaps a few are interrupted in the external arciform nucleus. The posterior external arciform fihers^^ rise from the same nuclei and enter the cerebellum, through the inferior peduncle, without decussation. Both groups of fibers end in the cortex of the vermis cerebelli superior. The internal arciform fibers are contained in the formatio reticularis. They are disposed in two groups, viz. : (18) Flbrse arcuatse. (19) Fibrse arcuatse externa anterior, posterior. 136 THE BRAIN AND SPINAL CORD. Those of the sensory decussation, and those of the olivary peduncle. The fibers of the Setisory Decussation^^ rise chiefly from the nucleus gracilis and nucleus cuneatus. Bending ven- trally through the posterior horn of gray matter, they decus- sate through the median raphe; and, then, the greater num- lier run forward toward the cerebrum as the interolivary fillet (medial and superior fillets) ; the remainder constitute the deep part of the anterior external arcifornp fibers. The sensory, or fillet, decussation is nearer the pons and dorsal to the decussation of the pyrami'ds. The Olivary Peduncle is a sheet of fibers extending between the two olivary nuclei of the medulla. It is the inferior por- tion of the cerehello-olivary tract?^ It is composed of axones from Purkinje's cells. Descending to the medulla through the inferior cerebellar peduncle, it pierces the olive, crosses through the raphe and terminates in the olivary body of the opposite side. The cerebello-olivary tract connects the cere- bellar hemisphere with the opposite nucleus. (2) The Dorso- ventral Fibers of the medulla are found in three situations: (a) In the raphe, (b) between the ante- rior and lateral areas, and (c) between the lateral and poste- rior areas. (a) The dorso-ventral fibers of the raphe are the ante- rior external arciform fibers. These can be traced to the cere- bellum through the restiform body. Their origin is chiefly in the nuclei gracilis et cuneatus. Some of them seem to be interrupted in the arciform nuclei on the ventral surface of the pyramids. The root-bundles of the eighth to the twelfth cranial nerves constitute the remaining groups of dorso- ventral fibers. By them the medulla is divided into areas. (20) Decussatio lemniscorum. (20 Fibrse cerebello-olivares. THE AFTER-BRAIN. 137 (b) The root-bundles of the hypoglossal nerve^^ run from the ventricular gray matter, near the median line, ventro- laterally to the ventro-lateral groove, where they emerge. In- closing between them and the raphe, the anterior area, they also separate it from the lateral area. The anterior and lateral areas are bounded dorsally by the thick sheet of gray matter in the floor of the fourth ventricle. (c) The medial root^^ of the auditory nerve, the roots of gJosso-pharyngeal^^ and vagv^^^ and the accessory root of the eleventh^^ form the third .group of dorso-ventral fibers. From the dorso-lateral groove, which is their superficial origin, they may be traced through the medulla to ventricular gray matter external to the column of cells from which the twelfth nerve rises. Tbey separate the lateral from the poste- rior area. The posterior area comprises everything dorsal to the above roots of the eighth to eleventh cranial nerves. It thus includes the gray matter in the floor of the fourth ven- tricle. (3) longitudinal Fibers. — In the medulla, the longitu- dinal fibers are chiefly continuations of the same in the spinal cord. They can be best located by reference to the three areas bounded by the above dorso-ventral fibers, namely. An- terior, Lateral and Posterior areas. ANTERIOR AREA. The anterior area of the medulla lies between the raphe and the roots of the hypoglossal nerve, and between the ventral surface and the gray matter in the floor of the fourth ventricle. Excepting that part forming the crossed pyram- idal tract and the interolivary fillet, it is continued in the (22) Nervus hypoglossus. (23) Radix nervi vestibularis. (24) Radix nervi glossopharyngei. (25) Radix nervi vagi. (26) Radix cerebralis nervi accessorii. 138 THE BRAIN AND SPINAL CORD. anterior column of the spinal cord. It is naturally divided into a ventral and a dorsal part, or the region of the pyra- niid27 and the region of the formatio reticularis alba. The Pyramid, with the arciform nucleus imbedded in it, and the arciform fibers winding over it, occupies the ventral portion of the anterior area. It is the continuation of the pyramidal tract and is composed of the axones of cortical cells in the Rolandic region of the cerebrum. The pyram- idal tract diminishes in size as it descends through the pons and medulla, because some of its fibers terminate in ramifica- tions about the cells of cranial nerve-nuclei. In the lower part of the medulla, the pyramid breaks up into the un- crossed (direct) pyramidal tracP^ (10 to 20 per cent of the pyramid), which descends along the anterior median fissure in the same side of the spinal cord; and the crossed pyram- idal tract^^ (80 to 90 per cent of the pyramid), which, after decussating with its fellow through the anterior median fissure, runs down in the lateral column of the opposite side of the cord. The fibers of the direct tract cross in succession to the opposite side of the cord, through the anterior, or white, commissure; and there, with the fibers of the crossed pyramidal tract, terminate in fibrillar end-tufts about the cell-bodies in the anterior comu of gray matter. Thus the pyramid forms a crossed cerebral tract for efferent (motor)~ cranial and spinal nerves. A small number of pyramidal fibers (20 per cent, Marchi) descend in the lateral column of the cord without decussation. They account for the weak- ness on the well side, and for slight motion on the paralyzed side, which are commonly observed in hemiplegia. (N. 15, Add.) (27) Pyramis meduUfe oblongatae. (28) Fasciculus cerebro-spinalis anterior (ventralis). ^29) Fasciculus cerebro-spinalis lateralis, THE AFTER-BRAIN. 139 The dorsal part of the anterior area is occupied by the formatio reticularis alha. Gray matter from the anterior horn is sparsely scattered throughout the reticular formation, but it contains the bodies of very few nerve cells and is of a light color. The intei^nal accessory olivary nucleus is im- bedded in it near the pyramid and among the fibers of the fillet; and three definite bundles of longitudinal fibers have been demonstrated in it, namely, the Interolivary Fillet, the Posterior and the Anterior longitudinal bundles. Interolivary Fillet. — ^Just dorsal to the pyramid in the anterior area of the medulla, is a large bundle of fibers called the interolivary fillet.^^ Situated between the inferior oli- vary bodies, it is on that account called the interolivary fillet. Superiorly, it is continued in the medial and superior fillets.^'^ The interolivary fillet rises from the nucleus gracilis and nucleus cuneatus of the medulla and crosses through the median raphe in the sensory decussation. As the fillet runs brain ward through the reticular formation of the pons and mid-brain, it receives fibers from the terminal nuclei of sensory cranial nerves, except the cochlear nuclei, and from the middle peduncles of the cerebellum. Externally, it is accompanied for a short distance in the pons by the lateral fillet.^2 The interolivary fillet is composed of ascending axones which constitute a "cerebral" tract for the afferent, or sensory, fibers of spinal and cranial nerves. It carries ordi- nary sensations to the superior quadrigeminal body by the superior fillet, and to the optic thalamus by the medial fillet. The Posterior Longitudinal Bundle^^ is a small fasciculus composed of fibers continued up from the anterior column of (30) Lemniscus interolivarls. (31) Lemniscus medialis et lemniscus supertar. (32) Lemniscus lateralis. (33) Fasciculus longitudinalis medialis. 140 THE BRAIN AND SPINAL CORD. the spinal cord. Its origin is in the anterior horn of gray matter. In the medulla it runs along the median raphe in contact with the ventricular gray matter, and is augmented in the medulla and pons by fibers from the terminal nuclei of the sensory cranial nerves and by fibers from the nuclei of the abducent nerves and the middle cerebellar peduncle. Further forward, some of these fibers and others of spinal origin leave the bundle to end, chiefly on the opposite side, in the motor cranial nerve-nuclei, especially the third. Fibers join the posterior longitudinal bundle in the mid-brain from the motor oculi nucleus, and descend to the genu of the facial nerve. The posterior longitudinal bundle ends, supe- riorly, in the thalamus or hypothalamus. It associates spinal and cranial nerves with one another, forming part of a reflex arc. It also connects the cerebellum with opposite cranial nuclei and probably conducts ordinary sensation to the thalamus (see Mid-Brain). Anterior Longitudinal Bundle. — The pupillo-dilator tract^* rises from the superior quadrigeminal body, and is seen just ventral to the posterior longitudinal bundle, which it accompanies all the way down to its chief termination in the ciliospinal centers of the cervical cord (see Mid-Brain). LATERAL AKEA. Contents: Superficially, the antero-lateral ground bundle and antero-lateral descending and ascending cerebellar tracts; Deeply, the formatio reticularis grisea. Imbedded in the formatio reticularis are the nucleus ambiguus, the lateral nucleus, the olivary nucleus and external accessory olivary nucleus. The gray matter of the formatio reticularis grisea is a (34) Fasciculus longltudinalis ventralls. THE AFTER-BRAIN. I4I part of the disintegrated anterior gray horn and, unlike that of the anterior area, it contains the bodies of many large nerve cells. Antero-lateral Ground Bundle.^^ — The whole lateral col- umn of the spinal cord, except the crossed pyramidal and direct cerebellar tracts, is continued into the lateral area of the medulla. Composed of ascending and descending axones which are commissural and associative for different segments of the spinal cord, the lateral ground bundle ascends into the medulla, and runs in part beneath and in part superficial to the olivary nucleus; beyond the olive, it is continued in the formatio reticularis grisea of the medulla and reticular formation of pons and mid-brain. Among the fibers of the antero-lateral ground bundle, ventral to the olive, is the tnangular tract^^ of Helwig and, dorsal to the olive, the olivary bundle. The former is believed to end in the olive of the medulla and the latter to rise from it. They are made up of ascending axones and, according to Bechterew, form a functionally continuous tract. The Antero-lateral Descending Cerebellar Tract^'^ rises in the cerebellar cortex. It forms part of the inferior peduncle of the cerebellum, through which it reaches the medulla. In the lateral area, it descends along the ventro-lateral groove, bet\^een the lateral tract and pyramid, to the corresponding area of the cord. It ends in the anterior cornu of gray matter. Fibers from the cerebral cortex are scattered through the bundle in the cord, and it was once regarded as ' a part of the direct pyramidal tract (N. 11, Add.). Antero-lateral Ascending Cerebellar Tract. ^'^ — Taking its (35) Fasciculus proprius antero-lateralls. (36) Tractus triangrularis (Helwlgi). (37) Fasciculus antero-lateralis superficialis, descendens and as- cendens. 142 THE BRAIN AND SPINAL CORD. origin from the base of the anterior cornu and center of the crescent of gray matter, chiefly on the opposite side of the spinal cord, and crossing through the anterior commissure, it ascends mingled with the fibers of the above descending tract, along the lateral surface of the cord. It runs along the dorso-lateral groove and through the formatio reticularis of the medulla and pons; and then, turning backward, it reaches the superior cerebellar worm through the valve of Vieussens. A small bundle of its fibers winds over the su- perior cerebellar peduncle, and joins the lateral fillet in its course to the inferior quadrigeminal body; that bundle ends in the optic thalamus. The antero-lateral ascending cere- bellar tract is closely related to the direct cerebellar tract. Both carry sensory impulses to the vermis cerebelli superior, though from different parts of the cord. The Crossed Descending Tract of the Red Nucleus, running dorsal to the inferior olive, is mingled with the fibers of the antero-lateral ascending cerebellar tract, in the medulla; it continues down the cord, in the dorso-lateral portion of the crossed pyramidal tract, to the lateral horn and center of the gray crescent as far as the first lumbar segment. POSTERIOR AREA. The longitudinal fibers of the posterior area form many bundles; and the bundles are different in upper and lower medulla. The formatio reticularis is small, but is present throughout this area. The lower, or closed, medulla contains: The Fasciculus gracilis,^^ Fasciculus cuneatus,^^ Fasciciilus of Eolando and Direct cerebellar tract (named from the posterior median fissure outward). In the upper or ventricular medulla are: (38) Fasciculus gracilis. (39) Fasciculus cuneatus. THE AFTER-BKAIN. 143 The Restiform body, at the surface; and the Inferior (or spinal) root of the fifth cranial nerve, the Fasciculus soli- tarius and Fasciculus teres in the interior. The Fasciculus Gracilis is the superior end of the postero- median column (GolFs column) of the spinal cord. Near its extremity it expands and forms the clava, and then tapers off and disappears along the side of the fourth ventricle. The clava is due to the nucleus gracilis, in which the fibers of the column end. A small number of fibers continue, without interruption, into the fillet and external arciform fibers. Like the cuneate column, the fasciculus gracilis is composed of ascending branches of the posterior roots of the spinal nerves. Fasciculus Cuneatu^. — It is 'separated from the posterior median fissure by the gracile bundle ; and is the continuation of the greater portion of the postero^lateral column (Bur- dach's column) of the spinal cord. It ends about the cells of the nucleus cuneatus and accessory nucleus cuneatus, which form the cuneate tubercle seen on the surface. A few fibers from this bundle are directly continued in the interolivary fillet, and two small bundles, inclosing the inferior (or spinal) root of the fifth nerve, run as posterior external ai-ei- form fibers to the cerebelliun. The fibers of the fasciculus cuneatus*^ are ascending hranches of the posterior roots of the spinal nerves. Fasciculus of Rolando. — From the cuneate column, a small bundle of fibers, taking a more lateral course, runs over and ends within the nucleus of Rolando. It constitutes the fas- ciculus Rolandi. This column is not separately represented in the spinal cord. The nucleus of Rolando, in which it terminates, is situated beneath the restiform body. The (40) Fasciculus cuneatus. 144 THE BRAIN AND SPINAL CORD. nucleus causes a slight eminence on the surface called the tuberculum Rolandi. The Direct Cerebellar Tract^^ in the lower medulla crosses the dorso-lateral groove, from the lateral column of the cord to the posterior area of the medulla; it then ascends to form a large part of the restiform body, the inferior peduncle of the cerebellum. It takes its origin from the vesicular col- umn of Clark in the spinal cord. It ends very largely on the opposite side in the superior cerebellar worm. Restiform Body.— In the upper medulla, forming the lateral part of each posterior area, is a large rounded bundle of fibers, called the restiform body.*^ n jg the largest bundle in the medulla. Forming the inferior peduncle of the cerebellum, it terminates in the cerebellar cortex of both the hemisphere and worm. It is made up of the following: Ascending — (1) Direct cerebellar tract; (2) External arci- form fibers, anterior and posterior; (3) The acustico-cere- bellar tract from the nuclei of the vestibular nerve to the nucleus fastigii and nucleus globosus of the opposite side; and (4) A tract from the lateral nucleus to the same side of the cerebellum. Descending — (1) Antero-lateral descend- ing cerebellar tract, and (2) The cerebello-olivary tract, which ends in the inferior olive opposite to its origin. The restiform bodv is inclosed between the medial and lateral roots of the auditory nerve (eighth ).*3 Yentral to it and between the roots, is the ventral part of the cochlear nucleus; on its lateral surface and among the fibers of the lateral root, is the dorsal, or lateral, part of the same nucleus. The vestibular nuclei, the dorso-medial (Schwalbe), the dorso-lateral (Deiter), and the superior (Flechsig and (41) Fasciculus cerebello-spinalls. (42) Corpus restiforme. (43) Nervus acusticus. THE AFTER-BRAIN. I45 Beehterew) are situated dorsal and medial to the restiform body. The Inferior Root of the Fifth Nerve^^ is the main sensory root. It leaves the superior sensory root in the pons; and, running down in the lateral portion of the posterior area, it terminates ventral to the restiform body about the cells of the nucleus Rolandi. Fasciculus Solitarius. — The respiratory bundle is a small, round bundle imbedded in the middle of the ventricular gray matter of the posterior area. It forms an accessory sensory root for the ninth and tenth cranial nerves. It descends near the main nuclei of those nerves and along the medial aspect of the posterior horn of gray matter in the cord. It ends on both sides of the median line in the gray matter along its course. The solitary bundle may be traced from the upper part of the medulla down to the eighth cervical segment of the spinal cord (Cajal). Many of its fibers cross through the raphe and, after giving off collaterals to the interolivary fillet, terminate about cells on the opposite side. It is be- lieved to associate the nuclei of the nerves controlling the muscles of respiration, hence the synonym, respiratory bundle. Fasciculus Teres. — On either side of the median line and extending almost the whole length of the floor of the fourth ventricle, is a lozenge-shaped eminence, called the fasciculus teres. In the pontine part of the ventricular floor, it ends as the eminentia teres. It tapers off to a point in the posterior angle of the ventricle (hypoglossal trigone), and the two fasciculi form the nibs ol a pen, the calamus scriptorium. It is composed of a flat band of fibers covering the hypoglossal nucleus, posteriorly, and the terete and the abducent nucleus, (44) Radix spinalis nervi trigemini 146 THE BRAIN AND SPINAL CORD. anteriorly. The ascending portion (genu) of the root of the facial (or 7th) nerve and fibers from the forma tio reticularis make up the fasciculus teres. *- GRAY MATTER OF MEDULLA. The gray matter of the medulla is composed, (1) .of that continued up from the spinal cord, and (2) of addS nuclei not represented in the cord. (1) By the dilation of the central canal of the spinal cord forming the fourth ventricle, the posterior comua of the H-shaped column of gray matter are pushed outward to a transverse direction; and the bases of the anterior cornua are brought into the floor of the ventricle. The expansion of the canal, together with the decussation of the crossed pyramidal tracts through the anterior cornua and of the in- terolivary fillets through the posterior and anterior cornua, disposes the H-shaped Column as follows: Anterior Horn. — From the base of the anterior cornu*^ is derived a column of cells, the hypoglossal nucleus, which lies along the median raphe beneath the fasciculus teres. The head of the anterior cornu is broken up by the crossed pyramidal tract into the nucleus later-alis, in the lateral area, near the dorso-lateral groove; and the nucleus amhiguus, a large column of cells, coinciding in extent with the inferior olive, and seen as a pear-shaped mass in the lateral area, which is the motor nucleus for the ninth, tenth and access- ory part of the eleventh cranial nerves. The lateral nucleus is probably terminal to certain fibers in the antero-lateral ascending cerebellar tract, and it gives rise to a tract of fibers which runs through the restiform body to the cortex in the same side of the cerebellum. The gray matter of the formatio reticularis alba et grisea belongs to the anterior cornu. It is (45) Columna anterior. THE AFTER-BRAIN. 147 of a light color (alba) in the anterior area, where there are the bodies of but few cells. In the lateral area the cell- bodies are numerous and the color is gray (grisea). The Posterior Horn^^ is decapitated by the fillet. Its base forms a column of cells, external to the nucleus am- biguus and hypoglossal nucleus, which contains the chief sensory nucleus of the pneumo gastric (lOth), of the glosso- pharyngeal (9th), and of a part of the auditory (8th) nerves. It forms likewise the accessory cuneate nucleus. The head of the posterior horn forms the nucleus of Rolando. That nucleus is the inferior sensory nucleus of the trifacial (5th) nerve. In it the so-called ascending root of the fifth terminates. The posterior horn furnishes the gray matter for the reticular formation of the posterior area. It should be noted that the chief nuclei derived from the H-shaped column lie in the floor of the fourth ventricle. (2) Added Nuclei. — The medullary gray matter not rep- resented in the spinal cord makes up the following nuclei: Nucleus gracilis, nucleus cuneatus, olivary nuclei, and nu- cleus of external arciform fibers. Nucleus Gracilis and Nucleus Cuneatus. — They are situ- ated near the dorsal surface of the medulla, beneath the gra- cile and cuneate bundles, whose fibers terminate in them : they give origin to the interolivary fillet and the anterior and posterior external arciform fibers, the two former con- stituting the sensory decussation; and they produce, re- spectively, the clava and cuneate tuhercle.'^'^ The accessory cuneate nucleus is a continuation of the vesicular column of Clark at the base of the posterior gray horn in the spinal cord. From it a small fasciculus rises which, as posterior (46) Columna posterioF. (47) Tuberculum cuneatum. . 148 THE BRAIN AND SPINAL CORD, external arciform fibers, runs within the restiform body to the eerebellnm. The nucleus gracilis and cuneatus are connected with the posterior cornu, but have no representa- tive in the cord. The Olivary Nucleus^^ of the medulla (inferior olivary nucleus) is a sinuous, pouch-like collection of gray matter resembling the corpus dentatum of the cerebellum. It is situated near the lateral surface of the medulla and is in- vested superficially and deeply by fibers from the antero- lateral ground bundle. Its open hilum looks medially and is filled with fibers, the cerebello-olivary tract/^ which join it to the opposite hemisphere of the cerebellum. On either side of the olivary nucleus is an accessory nucleus — the in- ternal accessory,^^ in the anterior area among the fibers of the inter-olivary fillet, and the external accessory,^^ in the lateral area. The olivary nucleus, covered by fibers of the antero-lateral ground bundle, forms the olivary body (oliva). The triangular tract of Helwig, or the olivary bundle of the spinal cord, enters the ventral surface of the olivary body and is believed to terminate in it. The olivary bundle of the brain, the central tegmental tract, appears to rise from the olive in the medulla and to continue the ascending conduction tract to the globus pallidus of the lenticular nucleus (Flechsig). The latter tract is situated just dorsal to the olive. The inferior olive receives two tracts of descending fibers, namely, the vestibulo-olivary and the cerebello-olivary. And according to Koelliker, it gives origin to axones which descend through the lateral column of the spinal cord to the anterior gray cornu. (48) Nucleus olivaris inferior. (49) Pibrse cerebello-olivares. (50) Nucleus olivaris accessorius medialis. (51) Nucleus olivaris accessorius dorsalis. THE AFTER-BRAIN. 149 Nucleus of the External Arciform Fibers. — There are sev- eral masses of gray matter, containing the bodies of nerve cells, scattered among the anterior external arciform fibers. These form a large sheet-like mass on the ventral and medial surface of the pyramid. It is called the arciform nucleus,^^ and probably constitutes a relay for certain of the anterior external arciform fibers. The arciform nucleus is continuous above with the nucleus pontis. Lesions in the medulla are very fatal and death usually occurs before any sensory or motor phenomena can be ob- served; but rarely the pyramidal tracts alone have been in- volved or the pyramidal tracts together with one or more of the roots of the ninth to the twelfth cranial nerves. In the last case, crossed paralysis is produced, affecting the cranial nerves on the same side and the opposite spinal nerves. In progressive bulbar paralysis the motor nuclei of the medulla are involved as "a preliminary to the degeneration of the an- terior gray cornu in the spinal cord ( Grlossolabio-laryngeal paralysis). (52) Nucleus arcuatus. CHAPTER VII. FOURTH VENTRICLE. The common cavity of the hind-brain and after-brain is the fourth ventricle.^ The fourth ventricle is contained in the pons and medulla, and is ventral to the cerebellum. It is broadest at the junction of the pons and medulla. Above and below that junction, it contracts to the size of the aque- duct of Sylvius and central canal of the spinal cord, with which it is continuous. Dorsally, it communicates with the subarachnoid space through three foramina (Magendie, and Key and Retzius). It is a gable-roofed chamber with a dia- mond-shaped floor. The long axis of the floor is parallel with the spinal cord, and extends from the superior extrem- ity of the pons to the middle of the medulla. The trans- verse axis coincides with the junction of the pons and medulla. Thus the superior triangle of the floor is formed by the pons; the inferior, by the medulla oblongata. The fourth ventricle is lined with ependyma, which is complete throughout, except in the roof of the inferior part, where only the epithelial layer is present. Boundaries. — The floor is formed by the pons and me- dulla. The lateral walls (superior triangle) are formed by the superior peduncles^ of the cerebellum; and (inferior tri- angle) by the inferior cerebellar peduncles,^ fasciculus cuneatus and fasciculus gracilis. The roof is formed by the valve of Vieussens,* superiorly; and the inferior medullary (1) Ventriculus quartus. (3) Corpora restiformia. (2) Brachia conjunctiva. (4) Velum medullare anterius. FOURTH VENTRICLE. I5I velum and roof epithelium, inferiorly. The superior and inferior halves of the roof meet at an acute angle and form the tent^ of the fourth ventricle. On either side, the tent extends over the restiform body into the lateral recess. The lateral recess is a tunnel-like extension of the ventricular cavity. It is bounded, superiorly and ventrally, by the in- ferior cerebellar peduncle; dorsally, by the inferior medul- lary velum; and inferiorly, by the roof epithelium. The choroid plexuses^ of the fourth ventricle invaginate the roof epithelium and hang from the roof in the posterior part of the cavity. Floor of the Fourth Ventricle. — Because of the origin of one or more roots of the posterior eight (fifth to twelfth) cranial nerves from the floor of the fourth ventricle, it is a very important area. A median groove''' forming the long axis of the diamond-shaped floor, divides it in two lateral halves, which are bisected transversely by a number of lines, the acustic striae.^ The acustic striae are produced by bundles of fibers which rise from the cochlear root in part, but chiefly from the cochlear nucleus of the auditory nerve. Plunging into the median groove, the greater number enter the oppo- site trapezium and lateral fillet; the remainder, according to Koelliker, become anterior external arciform fibers. The acustic strias divide each lateral half of the floor into a su- perior and an inferior triangle. The Superior Triangle of the floor presents the eminentia teres, superior fovea, locus coeruleus and a part of the acustic trigone. (5) Fastigium. (6) Plexus choroideus ventriculi quartl. (7) Sulcus longitudinalis fossse rhomboidese. (8) Striae medullares. 152 THE BRAIN AND SPINAL CORD. The Emi/nentia Teres,^ the anterior extremity of the fascic- Tilus teres/ ^ is located next the median groove. Beneath it are the nucleus teres (accessory to ninth and tenth cranial nerves), and nucleus of the abducent (sixth) nerve. Ex- ternal to it and in front of the striae acusticae is a small fossa, the fovea superior. , The Fovea Superior. — The fovea superior is near the lat- eral wall of the ventricle and marks the location of the facial (seventh) nucleus, which is deeply seated in the pons. Run- ning forward and medially along the wall of the ventricle from the superior fovea, is a blue-floored groove, called locus coeruleus. The Locus Coeruleus continues to the anterior angle of the ventricle. The color of the locus coeruleus is due to the substantia ferruginea, a, pigmented layer of cell-bodies un- derlying it. The principal motor nucleus of the trifacial, or fifth, nerve lies beneath the anterior part of the locus coeruleus. Inferior Trianglei of the Ventricular Floor. — It presents: The hypoglossal trigone, trigonum vagi (fovea inferior, ala cinerea and eminentia einerea) and most of the trigonum acustici. The Hypoglossal Trigone^'^ is the inferior half of the fas- ciculus teres. Its apex is in the inferior angle of the ven- tricle, and forms a nib of the calamus scriptorius; its base looks upward and is situated under the acustic striae. The twelfth nerve rises from the column of cells covered by it. External to the trigonum hypoglossi and inferior to the acustic striae is the inferior fovea, which forms the apex of the trigonum vagi. (9) Colliculus facialis. (10) Eminentia medlalis. (U) Trlgronmn nervl hyposlosst FOURTH VENTRICLE. I 53 Trigonum Vagi. — The pneumogastric trigone is of a darker color than the ventricular floor around it, and is often called the ala cinerea. The inferior fovea forms the de- pressed and superiorly directed apex of the triangle ; its floor rises inferiorly to the base, eminentia cinerea, which abuts against the lateral wall of the ventricle. The principal nuclei of the glosso-pharyngeal (or ninth) and the pneumo- gastric (or tenth) nerves are situated, respectively, beneath the fovea inferior and trigonum vagi. The Trigonum Acustici^^ occupies the lateral angle of the ventricular floor. It is partly in the superior triangle, but chiefly in the inferior. Inclosed between the trigonum vagi and the ligula, its apex points downward, and its base looks upward and is crossed by the acustic striae. A slight tuber- cle, eminentia acusticce, makes the base of the trigone, in the lateral angle most prominent. Beneath the acustic tri- gone is the dorsal, or vestibular, nucleus of the auditory nerve; also the dorsal part of the cochlear nucleus, which is found in the acustic tubercle. ORIGIN OF CRANIAL NERVES. According to Soemmering, there are twelve pairs of cranial nerves. Their origins (or terminations) are superficial and deep. The meaning of Superficial (apparent) origin, as commonly used, is the point of attachment of a nerve to the brain or cord surface; Deep (real) origin signifies the deep- est point to which the fibers of a nerve can be traced. For Motor Nerves this nomenclature is correct, the deep origin being the nucleus in which the fibers rise that form the nerve; but it is exactly opposite to the truth for Sensory Nerves. The so-called deep origin of a sensory nerve is actually the terminal nucleus in which the fibers of the nerve (12) Area acustica. 154 THE BRAIN AND SPINAL CORD. arborize and end. With these facts in mind examine the following table (N. 12, Add.). Name. 1. Olfactory". (Smell) TABLE II. Superficial origin, or termination. Deep origin, or termination. Nerves . Olfactory f Stratum glomeru- bulb, surface • • • "S losum of olf ac- . L tory bulb. Gyrus fornicatus. Trigonum olfac- torii. Uncus hippocam- pi. Tract. Three roots 2. Optic".... (Sight) Nerve. Optic commissure . . . Optic tha- lamus, ex- ternal and internal geniculate bodies, an- t e r i o r q uad r i- geminal body Tract 3. Oculomotor". (Motor) 4. Trochlear". (M.) Interpeduncular fossa Outer root — Ex- ternal geniculate body, optic tha- lamus, Anterior quadrigeminal body. Inner root — Optic thalamus, Inter- nal geniculate body. Floor of Sylvian aqueduct. Valve o f sens . . . Vieus { Floor of Sylvian aqueduct. (13) Nervus olfactorius. (14) Nervus opticus. (15) Nervus oculomotorius. (16) Nervus trochlearis. FOURTH VENTRICLE, 155 5. Trifacial".... (M. Sensory) 6. Abducent". (M.) 7. Facial" (M.) Pars intermedia-". (Taste) Pons, ventral sur- face Groove between pons and me- dulla Groove between pons and me- dulla Between facial and auditory. 8. Auditory^^ (Hearing and space-sense) { Groove between pons and me- dulla , Motor root — Floor of fourth ventri- cle, and Sylvi- an aqueduct. Sensory root — Under superior cerebellar pe- duncle in pons, and Nucleus of Rolando in me- dulla. Floor of fourth ventricle be- neath eminentia teres. Floor o f fourth ventricle be- neath superior fovea. Beneath inferior fovea. r Vestibular root — Vestibular (or Dorsal) nucleus in ventricular floor, Spinal nu- cleus in cord. Nucleus fastigii and nucleus glo- bosus in cerebel- lum. Cochlear root — Cochlear (or ventral) nucle- us (ventral and dorsal parts) in dorso - lateral groove and on lateral surface of restiform body, and various nu- clei up to pos- terior quadri- geminal body. (17) Nervus trigeminus. (18) Nervus abducens. (19) Nervus facialis. (20) Nervus intermedius, (21) Nervus acustious. 156 THE BRAIN AND SPINAL CORD. 9. Glossopharyngeal^^ <^ groove of me- Ventricular floor, (M. S. and I dulla J posterior trian- {Dorso-lateral . ^ groove of me- dulla inal veins.^° The membranes of the spinal cord are sup- pilied by recurrent branches of the spinial nerves and by ibe sympathetic. (8) Arteria spinalis anteFior. (9), Aa. spinales posteriores. (10) Venae spinales externse. CHAPTER IX. THE SPINAL CORD. The spinal cord^ is developed from the posterior part of the neural tube, and forms the corresponding portion of the central axis of the nervous system. Extent. — It is continuous with the medulla oblongata, above; and, in the adult, reaches to the lower border of the first lumbar verticbra. Its length is seventeen to eighteen inches. In a very slender process, the filum terminale, the cord is continued beyond the first lumbar vertebra. That process and the lower spinal nerves form the cauda equina, which is inclosed in a sheath composed of the arachnoid and dura mater. The filum terminale, for some distance, con- tains a prolongation of the central gray matter and ventricle of the cord; and, also, a few fibers, which suggest the coccy- geal nerves of lower animals. In the foetus before the third month, the cord and spinal canal are of equal length. At birth the cord reaches the third lumbar vertebra, and it continues to recede with the rapid growth of the vertebra to adult life. Size. — ^The spinal cord is shaped like a cylinder, slightly flattened from before backward (dorso-ventrally). Its long- est diameter is transverse and measures less than half an in;ch, except in the cervical and lumbar enlargements of the cord. In the latter, it equals a half -inch ; and, in the former, it slightly exceeds it. The thoracic portion of the cord is (1) Medulla spinalis. THE SPINAL CORD. E63 small and nearly cylindrical in shape. Divested of its meninges and nerves the spinal cord weighs about one ounce and a half avoirdupois. The cervical enlargement^ extends from the medulla ob- longata to the second thoracic vertebra. Its greatest diana- eter is on a level with the fifth intervertebral disk. It gives origin to the nerves which form the cervical and brachial plexuses. The lumbar enlargement^ begins at the tenth thoracic vertebra and increases to the twelfth. Opposite the first lumbar vertebra, it tapers off almost to a point, the conus iepniinalis,^ but a very smadl process continues in the filum terminale. From the lumbar enlargement rise the nerves forming the lumbar and sacral plexuses. Sixth Ventricle. — ^The central canaP of the spinal cord is the representative of the cavity of the neural tube. It is just visible to the naked eye; but it extends throughout the cord and expands above into the fourth ventricle. In the filum terminale, it is also dilated, forming the inferior rhomhoid fossa.^ It is lined with columnar ciliated cells which stand on a thick lamina of substantia gelatinosa Rolandi. SURFACE. Fissures of the Spinal Cord. — The spinal cord is incom- pletely divided into symmetrical lateral halves by the an- terior and the posterior median fissure. The Anterior Median Fissure'^ is the broader and shallower of the two. It extends in length from the posterior end of the ventral surface of the pons (foramen caecum of Yicq d^Azyr) down the anterior median line of the medulla and (2) Intumescentia cervicalis. (5) Canalis centralis spinalis. (3) Intumescentia lumbalis. (6) Fossa rhomboidea inferior. (4) Conus medullarls. (7) Flssura mediana anterior. r64 THE BRAIN AND SPINAL CORD. cord, x'^s to depth, it equals one-third of the cord's axis. Its floor is formed by the anterior, or white, commissure. Both layers of pia mater dip down into it and inclose the anterior spinal artery and its branches. The anterior median fissure is interrupted at the junction of the cord and medulla by the decussation of the pyramids. In the lumbar enlargement it gradually disappears. The Posterior Median Fissure^ is narrow and deep. It extends, longitudinally, down the posterior median line of the cord from the middle of the dorsal surface of the medulla. It divides the cord, dorso-ventrally, beyond its middle. The floor of the fissure is formed by the posterior, or gray, com- missure, which, with the white commissure, separates the posterior from the anterior median fissure. The posterior median fissure is occupied by a lamina of connective tis- sue, the posterior septum, which is attached to the deep layer of the pia mater. In the posterior septum ramify branches of the two posterior spinal arteries and tributaries of the meduUi-spinal veins. Postero-lateral Fissure. — Each lateral half of the spinal cord is partially divided, near the junction of the posterior fourth with the anterior three-fourths of its semicircumfer- ence, by the postero-lateral fissure.^ The fissure is situated opposite the posterior cornu of gray matter, to which it trans- mits the posterior roots of the spinal nerves. It is continu- ous above with the dorso-lateral groove of the medulla. It separates the posterior surface and the antero-lateral sur- face from each other. Antero-lateral Fissure. — It is convenient to regard the narrow longitudinal area, through which issue the anterior roots of the spinal nerves, as the antero-lateral fissure. The (8) Fissura mediana posterior. (9) Sulcus lateralis posterior. THE SPINAL CORD. I65 anterior toots do not emerge in line one above another, nor is there any groove on the surface of the cord; thus the so- called fissure cannot be exactly located. It is situated op- posite the anterior cornu of gray matter and in line with the ventro-lateral groove of the medulla oblongata. It sub- divides the antero-lateral surface into anterior and lateral surfaces. The Postenor Intermediate Furrow^^ is a slight longi- tudinal groove which subdivides the posterior surface into postero-median surface and postero-lateral surface. From it a connective tissue septum extends into the cord and sepa- rates the columns of Goll and Burdach from each other. The posterior intermediate furrow is found only in the upper part of the cord, in the cervical and dorsal regions. The spinal cord is composed of (1) GTray matter, in the central part; and (2) White matter, in the peripheral area. It is like the medulla and pons in having the white matter on the surface. 1. Gray Matter of the Cord. A column of gray niatter,ii crescentric in section, extends throughi the center of each lateral half of the spinal cord. The crescent is convex medially; and is joined to its fellow, a little in front of the middle, by a transverse lamina of gray matter, called the posterior commissure}'^ It is joined to the white matter of the opposite side by the anterior com- missure.^^ The points of the crescent are directed forward and backward, respectively, and form the anterior and pos- terior cornua}"^ Together, the two crescents and the gra;y (10) Sulcus intermedius posterior. (11) Substantia grisea (12) Commissura posterior et c. anterior grisea. (13) Commissura anterior alba. (14) Columnse anteriores and c. posteriores. l66 THE BRAIN AND SPINAL CORD commissure form an H-shaped column of gray matter. The H-shaped column is well marked in the cervical and thoracic regions; but, toward the lower end of the cord, the crescents become short and thick and the gray column is almost cylin- drical. The gray matter of the cord is of two kinds: (1) The substantia gelatinosa Eolandi, which forms (a) a cap for the head of the posterior cornu and (b) an envelope for the central canal, or ventricle, of the cord. (2) The substantia spongiosa. The latter forms all the H-shaped column except the tips of the posterior horns and the thick sheath of the central canal. Imbedded in the neuroglia, there is a network of medullated nerve fibers, running longitudinally, dorso- ventrally and transversely, which gives it a spongy appear- ance under the microscope. Gray Crescent. — It is made up of (1) The Anterior Cornu ;i^ (2) The Center,^^ which is joined to its fellow of the opposite side by the gray commissure; and, (3) The Pos- terior Cornu.i''' There is a lateral projection from the base of the anterior cornu in the cervical and upper dorsal region, called the lateral horn}^ The reticula, or processus retic- ularis, forms a lateral projection from the base of the pos- terior cornu. It is found in the cervical region. (1) The Anterior Cornu^^ is short and thick compared with the posterior cornu. It is thickest in the cervical and lumbar enlargements; in the mid- thoracic region it is more slender. It does not reach the surface of the cord as does the posterior cornu. It ends in a bulbous, serrated head, which points toward the antero-lateral fissure. From it the anterior (15) Columna anterior. (16) Substantia intermedia grisea. (17) Columna posterior. (18) Columna lateralis. THE SPINAL CORD. 167 roots of the spinal nerves rise; and, together with the an*- terior root-fihers, it separates from each other the anterior and lateral white colnmnsi^ of the cord. Cells. — The anterior cornu contains two columns of large vesicular eell-bodiesy^o a medial and a lateral column. These columns are continuous throughout the cord. Their axones compose the greater part of all anterior roots of the spinal nerves. From the lateral column, and from a part of the medial, the axones enter the spinal nerves of the same side; the remainder pass through the anterior (white) commis- sure^i to the opposite nerves. They are distributed to the muscles of the trunk and extremities. Those neurones whose centers are in the medial column are believed to innervate the dorsal muscles of the trunk. The muscles of the ex- tremities are innervated by th^ dorso^lateral column; the ventral muscles of the trunk, by the ventro -lateral column. In the cervical region, the ventro-lateral column gives origin to the phrenic and spinal accessory nerves (Quain). The end tufts of the pyramidal fibers and of the descending cerebellar fibers are in relation with the dendrities or bodies of the cells of the anterior cornu. Fibers from the pos- terior roots of the spinal nerves and from cell-bodies within the cord, likewise, terminate in relation with them. The cells of the anterior cornu are both motor and trophic ( ?). Lesions. — The cells in the anterior cornu are the seat of hemorrhagic inflammation and rapidly degenerate in acute anterior poliomyelitis: in progressive museularr atrophy and in amyotropljic lateral sclerosis they degenerate slowly. As a result of the first, sudden paralysis occurs. The muscles waste away in the second and third because the nerves con- (19) Funiculus anterior and funiculus lateralis. (20) Perikaryons. (21) Commissura anterior alba. l68 THE BRAIN AND SPINAL CORD. trolling the muscles and their blood supply are gradually destroyed. In the last, the muscles are also spastic, because, as we shall see farther on, the involvement of the pyramidal tracts cuts off cerebral inhibition. (2) The Central Part of the Crescent^^ is both afferent and efferent. In it are located important reflex centers, such as, the Cilio-spinal, Secretory, Yaso-motor, Visceral, Geni- tal, etc. In the lumbar enlargement are centers of defeca- tion, micturition, erection, ejaculation, parturition; in the cervical enlargement the cilio-spinal, cardio-accelerator, etc., are found. The center of the crescent contains three columns of cell-bodies: The intermedio-lateral column of large vesic- ular cell-bodies,23 situated near the lateral surface . of the crescent; the middle column (Waldeyer), deep in the cres- cent at the junction of the gray commissure; and the dorsal column of Clark,^* which is situated near the inner surface of the base of the posterior comu. The neurones of the central part of the crescent axe largely sympathetic; this is especially true of Clark's column and to less extent of the intermedio-lateral column. The intermedio-lateral column is best marked in the thoracic region ; but is also found in the cervical and lumbar cord. Its cell-bodies,23 which are large and vesicular, are in relation with end-tufts of fibers from the posterior roots; and they give rise to efferent fibers that enter the anterior roots of the spinal nerves. Those fibers are probably sympa- thetic and supply the muscles of the glandular and circu- latory systems (Morris). Other axones from this column enter the antero-lateral ascending cerebellar tract. (22) Substantia intermedia grisea. (23) Perikaryons. (24) Nucleus dorsalis. THE SPINAL CORD. 169 The middle column (Waldeyer) is composed of mediiim- sized neiirone-centers,23 which are most abundant in the cervical region, where this column is best shown. Fibers from the posterior spinal roots have been traced into the column and probably the cell-bodies give rise to some of the fiber-s of the antero-lateral ascending cerebellar tract. But very little is certainly known of the function of this column. Clark's column (nucleus dorsalis) is continuous only through the thoracic region; but it is represented by the nuclei of Stilling in the cervical and lumbar regions and, in the medulla oblongata., by the accessory cuneate nucleus. Clark's cells are in relation with the end-tufts of fibers from the posterior roots of the spinal nerves. The axones of Clark's cells form the direct cerebellar tract, and help to form the anterior roots of the spinal nerves. The latter are sympathetic fibers, anabolic and inhibitory in function. They are distributed to the blood vessels, glands and muscu- lar coat of the alimentary canal (Morris). (3) The Posterior CornuJ^^ except in the lumbar cord, is slender. It is longer than the anterior cornu and reaches the surface in the postero-lateral fissure, where it receives the posterior roots of the spinal nerves. The posterior cornu presents a slight enlargement near its extremity^ called the caput cornuj^^ which tapers off to the apex cornu.^'^ The head is joined to the base of the horn by a constricted part, the cervix.^^ The head of the posterior horn is capped by the substantia cinerea gelatinosa of Rolando. The posterior corpu separates the posterior^^ from the lateral column^^ of the cord. The cells of the posterior cornu are very numerous. They (25) drolumna posterior, (28) Cervix columhge posterioris. (26) Caput columnae posterioris. (29) Funiculus posterior. (27) Apex columnse po&terioris. (30) Funiculus lateralis. I/O THE BRAIN AND SPINAL CORD. have smaller bodies than the cells of the anterior cornu and are less definitely grouped. In function they are afferent and associative. They are classified as follows: (a) The periph- eral cells, having a body and one long process, the comet cells (Waldeyer) ; (b) the central cells; (c) the basal cells; (d) the cells of the substantia gelatinosa, which have small and round bodies (Gierke and H. Yirchow) ; and (e) the solitary, fusiform-bodied cells, scattered throughout the pos- terior horn. The dendritic processes of the cells of the pos- terior cornu probably ramify in the gray matter adjacent to them. The axones run in various directions, viz., into the ground bundles, forming the septomarginal and cornu com- missural tracts, and, perhaps, the comma tract; into Bur- dach's column; into the center and anterior cornu of the same side; and, very largely, into the gray crescent of the opposite side. These last fibers, together with the antero- lateral ascending cerebellar tract, account largely for the immediate crossing of the main sensory path. Many fibers from the posterior roots of the spinal nerves terminate in ramifications about the cells of the posterior cornu on both sides, viz. : Those axones, forming the lateral group of small fibers in the posterior roots of the spinal nerves, end in relation with the small, round cell-bodies in the substantia gelatinosa Rolandi; other fibers end about the peripheral, the central, the basal and the solitary cell-bodies. The Posterior, or Gray, Commissure^^ completes the gray matter of the cord. It unites the two gray crescents together a little in front of their center, except in the lumbar region where it joins their centers. It forms the fioor of the pos- terior median fissure ; and, in front, is in relation with the white commissure. It is pierced longitudinally by Hie cen^ (31) Cotnmlssura anterior grlsea, and c. posterior. THE SPINAL CORD. I7I tral canal of the spinal cord, around which is a thick en- velope of substantia gelatinosa. That part of the commissure in front of the canal and that behind it are frequently described as the anterior and posterior gray commissures. The posterior commissure is composed of neuroglia in which are imbedded the bodies of many nerve cells and a large number of medullated fibers. The medullated fibers are de- rived from the posterior roots of the spinal nerves, and from intrinsic neurones of the cord, whose centers are situated chiefly in the commissure and in the posterior cornu. The commissure contains a long sensory tract between the ven- tricle and dorsal surface (Ciaglinski). The long sensory tract is found in the thoracic portion of the cord and the discoverer believes it to be made up of ascending root-fibers which conduct pain and temperature impulses. It is in need of further investigation. 2. White Matter of the Coed. The white matter^^ ^f ii^q spinal cord is disposed in its peripheral area and in the anterior commissure.^^ It is com- posed of medullated nerve fibers (axones and collaterals) imbedded in a small amount of neuroglia; and, like the gray matter, it is richly supplied with blood vessels. It is also supported by a connective tissue network derived from the pia mater. The fibers run transversely, dor so-ventr ally and longitudinally. Transverse fibers are found running between the longi- tudinal columns and the gray matter, or vice versa, and are continuous with the longitudinal fibers. The most definite lamina of transverse fibers is the anterior commissure. The Anterior, or White, Commissure. — It connects the an- (32) Substantia alba. (33) Commissura anterior alba. \y 172 THE BRAIN AND SPINAL CORD. terior and lateral white columns of the cord with the op- posite gray crescent. It is located in front of the gray commissure, and forms the floor of the anterior median fis- sure. It is composed of medullated fibers belonging to (a) the direct pyramidal tract, (b) the antero-lateral ground bundle, (c) the antero-lateral ascending cerebellar tract, and (d) of the crossed fibers to the anterior roots of the spinal nerves. The dorso-ventral fibers of the spinal cord are those of the anterior roots of the spinal nerves, in their course from the gray matter to the surface of the cord; and of the pos- terior roots, running from the postero-lateral fissure to their destination in the gray matter. The Longitudinal Fibers comprise most of the white matter in the cord, forming the funiculus anterior, funiculus later- alis and funiculus posterior. They are disposed around the gray crescent in bundles or tracts. The tracts are not visible to the naked eye, nor under the microscope in a healthy adult cord; they have been located by embryological, experimental and pathological investigations. The longitudinal fibers rise in the brain, in the spinal cord and in the spinal ganglia; some run upward and others downward, constituting the tracts of the cord. Thus the tracts are characterized as ascending, descending and mixed tracts. Ascending Tracts: (1) Antero-lateral ascending cere- bellar tract, (2) Direct cerebellar tract, (3) Postero-lateral tract, (4) Postero-median tract, (5) Marginal tract of Lis- sauer, (6) Posterior longitudinal bundle, (7) Olivary bundle (Hel wig's), and (8) Ciaglinski^s long sensory tract, in the gray commissure. Descending Tracts: (1) Uncrossed (direct) pyramidal tract, (2) Crossed pyramidal tract, (3) Antero-lateral de- scending cerebellar tract, (4) Comma tract, (5) Septomar- THE SPINAL CORD. 173 oinal tract; (6) Cornu commissural tract, (7) Anterior longitudinal bundle, and (8) Crossed descending tract of the red nucleus. Mixed, Ascending and Descending, Tract. — The Antero- lateral ground bundle. The Large Tracts of the Antero-lateral Columns^ of the spinal cord are seven in number, viz., the antero-lateral ground bundle, two pyramidal tracts, three cerebellar tracts and the marginal bundle of Lissauer. The antero-lateral ground bundle^^ occupies the deep part of the column. It embraces the anterior cornu of gray mat- ter and covers the outer surface of the center of the crescent and the base of the posterior cornu. It approaches, but does not quite reach, the surface of the cord. It is separated from the anterior median fissure by the uncrossed (direct) pyram- idal tract; the antero-lateral descending and ascending cerebellar tracts run between it and the surface of the cord; and, behind, it is in relation with the crossed pyramidal tract. The antero-lateral ground bundle is composed of ascending and descending fibers. It is a short fiber tract, associative and commissural in function. That part situated in the anterior column is largely commissural, between the anterior cornua; while the part in the lateral column is chiefly asso- ciative, and connects different segments of the cord on the same side. The antero-lateral ground bundle is continued in the formatio reticularis of the medulla, pons and mid- brain, constituting a short fiber tract which extends from the lower part of the cord to the basal ganglia of the cerebrum- Some of its ascending fibers form the posterior longitudinal hundle,^^ and extend up to the motor cranial nuclei and (34) Funiculus antero-lateralis. , (35) Fasciculus proprius antero-lateralis. (36) Fasciculus longitudinalis medialls. 174 THE BRAIN AND SPINAL CORD. hypothalamic region. Imbedded in the tract, also, between the anterior and lateral areas, is seen the anterior longitu- dinal hundle^'^ as far as lumbar cord (Barker). The latter runs from the superior quadrigeminal body to the cilio-spinal and other centers. The uncrossed (direct) pyramidal tract (Turck^s col- umn) ^^ occupies a thin area next the anterior median fissure. It is a continuation of the same tract in the medulla. Its fibers are axones of cortical cells whose bodies are situated in the Eolandic region of the cerebrum. " As the tract descends in the cord, the fibers decussate through the anterior commis- sure, and terminate in relation with the cells of the opposite anterior cornu. (N. 15, Add.) The antero-lateral descending cerebellar tract (Marchi and Loewenthal's column), ^^ together with the ascending antero-lateral cerebellar tract, occupies a thin peripheral area, broadest posteriorly, which extends from the direct pyramidal teact outward and backward, over the antero-lateral ground bundle, to the middle of the lateral surface of the cord. Its posterior border is in relation with the direct cerebellar tract and the crossed pyramidal tract. The fibers of the two tracts are mingled together; but the descending fibers are found, chiefiy, in the anterior part of the common area and the ascending in the posterior part. The descending fibers are axones from the cortical cells (Purkinje's) of the cerebellum. They descend to the spinal cord through the inferior cere- bellar peduncle and the lateral area of the medulla and, probably, end in the anterior cornu of gray matter. The descending cerebellar tract forms one segment of an indirect motor path (N. 11, Add,). (37) Fasciculus ventralis. (38) Fasciculus cerebro-spinalis anterior. (39) Fascicularis antero-lateralis superficlaHs (descettdens-ascen- dens). THE SPINAL CORD. 175 Antero-lateral ascending cerebellar tract (Column of Gowers).^^ — It is found chiefly in the posterior part of the area common to it and the descending tract. It is composed of axoriic processes of cells whose bodies are situated in the center of the crescent and base of the anterior comu, chiefly on the opposite side of the cord (v. Lenhossek). Most of the fibers of the antero-lateral ascending cerebellar tract cross near their origin through the anterior commissure of the cord. In the medulla,, the tract ascends through the dorsal part of the lateral area, sending collaterals to the lateral nucleus ; it then continues, through the formatio reticularis of the pons, to a point near th^- inferior quadrigeminal body, where it is bent backward over the superior ' cerebellar peduncle, and enters the vermis cerebelli superior through the valve of Vieussens (Hoche). According to Mott, two small bundles leave this tract at the angle, and run near the lateral fiilet to the superior corpus quadrigeminum and optic thalamus. Gowers' tract - carries thermic and pathetic impulses. The olivary bundle of the cord, the triangular tract of Helwig, is found near the middle of the area common to the antero- lateral cerebellar tracts ; it may be traced to the lumbar region, where its longest fibers rise. It ends in the olive of the medulla oblongata and is afferent in conduction. The direct cerebellar tract (dorso-lateral cerebellar tract) ^^ runs posterior to the antero-lateral tracts. It is superfitially located, and extends from the middle of the lateral surface of the cord back to the postero-lateral fissure, except in the lumbar cord. There its absence allows the crossed pyramidal tract to come to the surface. The direct cerebellar tract terminates in the superior worm of the cere- bellum. In the medulla, it forms a part of the restiform (40) Fasciculus cerebello-splnalU. 176 THE BRAIN AND SPINAL CORD. body. Its fibers are axones of Clark's vesicular cells. Th&y convey impulses of equilibrium received, especially, from the viscera. The crossed pyramidal tract^^ forms a considerable part of the lateral column of the spinal cord. It is covered, superficially, by the cerebellar tracts in the cervical and dorsal cord; but in the lumbar cord, it forms part of the surface. Its deep surface is in relation with the posterior comu of gray matter, the antero-lateral ground bundle and marginal bundle of Lissauer. The fibers composing it are axones of cell-bodies in the Rolandic region of the cerebral cortex. They rise with those of the uncrossed (direct) pyram- idal tract ;^2 ^nd the two run as one tract down through the genu and anterior two-thirds of the posterior segment of the internal capsule, the middle three-fifths of the crusta, the ventral longitudinal fibers of the pons and the pyramid of the medulla. In the medulla the two tracts separate. The crossed tract decussates with its fellow through the anterior median fissure, pierces the anterior gray cotnu and descends in the lateral column of the cord. It terminates in relation with the cell-bodies of the anterior comu. The uncrossed tract follows the anterior median fissure as already described. Both end chiefly in the anterior gray comu opposite to their cortical origin. According to Marchi, about twenty per cent of the fibers remain uncrossed. The pyramidal tracts are the cerebral motor tracts. By them motor and inhibitory impulses are carried to the cord. In the dorso-lateral, part ■of the crossed pyramidal area is found the crossed descending tract of the red nucleus. It extends as far as the first lumbar segment and ends in the center of the gray crescent. It is efferent in function. (N". 15, Add.) (41) Fasciculus cerebro-splnalis lateralis. (A2) Fasciculus cerebro-spinalis anterior. THE SPINAL CORD. 1/7 Lesions. — The pyramidal tracts (especially the crossed) are involved in lateral sclerosis and in amyotrophic lateral sclero- sis ; and, as a consequence of it, both voluntary and inhibitory impulses from the brain are interfered with, hence the spastic paralysis and exaggerated reflexes. The pyramidal tract may be more or less involved in insular sclerosis and in bulbar paralysis, and the symptoms vary with the amount of sclerosis. Gliosis of the pyramidal and cerebellar tracts and the posterior tracts (Dejerine and Letulle) has been demon- strated in Friedrich's hereditary ataxia, and the involvement of the pyramidal tracts explains the spastic paralysis which affects both the arms and legs. In ataxic paraplegia (Gowers) there is diffuse sclerosis of the lateral and posterior columjis of the cord. It is the degeneration in the pyramidal tracts that causes the spastic gait, incoordinated arm move- ments and early increase of the reflexes, observed in that affection. The marginal tract of Lissaiier*^ is a small tract com- posed of ascending branches of the outer set of fibers in the posterior roots of the spinal nerves. It is situated on the lateral surface and apex of the posterior cornu. Its fibers, after ascending a short distance, end about the cell-bodies of the substantia gelatinosa Rolandi. Tracts of the Posterior Column of the Cord.^* — There are three tracts in this column, viz., the postero-lateral, the postero-median and the ground bundle, or fasciculus pro- prius, which may be divided into the comma tract, septo- marginal tract and cornu commissural tract. The last three are descending tracts. Postero-lateral tract (Burdach's column) .^s — It runs up- ward just medial to the posterior cornu of gray matter. It is (43) Fasciculus marginalis. (45) Fasciculus cuneatus. (44) Funiculus pasterior. 178 THE BRAIN AND SPINAL CORD. made up of ascending branches of the posterior roots of the spinal nerves and of intrinsic fibers whose cell-bodies are in the gray matter of the cord. It become^ the fasciculus cunea- tus and fasciculus Rolandi, in the medulla; and it ends chiefly in the cuneate and Eolandic nuclei. A certain number of its fibers are continued directly into the interolivary fillet and others into the arciform fibers without interruption ; and some of the fibers of Burdach's column end in the gray matter of the cord as they ascend. In the midst of the postero-lateral tract, in the cervical and upper thoracic cord, is a small bundle of descending fibers, the comma tract; in the lumbar and sacral segments are found two descending tracts, the septomarginal and the cornu commissural. The two latter tracts are entirely intrinsic, and there seems to be no doubt that the comma tract is in part so, as some of its fibers degenerate after section either of the posterior roots of the spinal nerves or destruction of the posterior horn of gray matter. Burdach's column conveys all kinds of common sensory impulses (N. 13, Add.). The Cornu Commissural Tract is placed between the pos- terior cornu, the gray commissure and posterior septum. It extends up to the eleventh thoracic aegment. Septomarginal Tract (Bruce and Muir). — ^This tract is a semi-oval tract next the posterior septum in the third lumbar segment (Flechsig) ; and a triangular tract bounded by the septum and dorsal surface of the cord in the fifth sacral segment (triangle median, Gombault and Phillipe). The Comma Tract. — It is conuna-shaped in section, the head being directed forward. It is composed of descending branches of the posterior roots of the spinal nerves, and of intrinsic fibers of the spinal cord. It is considerably inter- mingled with fibers of the postero-lateral tract, and its termination is in the posterior cornu of the cord. THE SPINAL CORD. 1/9 The postero-median tract (GolFs column) ^^ ascends be- tween the postero-lateral tract and the posterior median septum. Like the postero-lateral tract in the cervical region, it extends in depth ventrally to the gray commissure. It is composed of ascending branches of the posterior roots of the spinal nerves. Continued into the medulla oblongata, the postero-median tract becomes the fasciculus gracilis. It ter- minates at the clava, the fibers ending in relation with the cell-bodies of the nucleus gracilis. A number of fibers, diverging from the tract, end in the gray matter of the spinal cord, and a few, without interruption, continue in the inter- olivary fillet to the thalamus and in the arciform' fibers of the medulla to the cerebellnm. GoU's column carries im- pulses of the muscular sense, and is particularly involved in locomotor ataxia. AH varieties of impulses, of bodily sensa- tion are carried by Bur dachas column. Lesions in the posterior colunm® cause disturbances of sensation, loss of reflexes and impaired equilibration. These columns are usually involved, by extensions from the pos- terior roots, in loeomotor ataxia (posterior sclerosis), hence the parsesthesia, crises, loss of reflexes, contracted pupil, dis- turbed equilibrium and ataxic gait. • They may be involved in insular sclerosis, and the sensory symptoms depend upon the extent of their degeneration. Section of the posterior column on one side in any segment of the spinal cord pro- duces, on the same side, more or less loss of sensation in that part of the body supplied by the segment cut, and, on the opposite side, complete anaesthesia below the section. ROOTS OF THE SPINAL NERVES. Thirty-one pairs of spinal nerves rise from the side of the cord. Each nerve has two roots: an anterior, efferent or (46) Fasciculus gracilis. l80 THE BRAIN AND SPINAL CORD. motor, root and a posterior, afferent or sensory, root. These roots descend more or less from their origin to the inter- vertebral foramen in which they unite to form the spinal nerve. The roots of the first cervical nerve are horizontal; those of the first dorsal nerve descend the width of two ver- tebras, and those of the twelfth dorsal, the width of four vertebrae; while the roots of the coccygeal nerve extend from the first lumbar vertebra to the second piece of the coccyx, through ten vertebrae. Anterior Root. — In all spinal nerves, except the first, the anterior root"^^ is smaller than the posterior.*^ It is com- posed of from four to six fasciculi, which soon combine into two bundles. After piercing the dura mater, the anterior root unites with the posterior, beyond the latter's ganglion, and forni'S a spinal nerve. It is efferent, or motor, in function. Super ficml (apparent) Origin. — The anterior root is com- posed of medullated axones which issue from the narrow longitudinal area commonly called the Antero-lateral Fissure. Deep (real) Origin. — The medullated axones rise from the Medial, Lateral, Clark's and Intermedio-lateral columns of cell-bodies on the same side, and from the Medial column of the opposite side. Lesions. — The lower motor neurones (spinal and cranial) are probably in a state of toxic irritation in laryngismus stridulus, tetanus, acute ascending paralysis (Landry), strychnine poisoning, etc., hence the twitchings, spasms and convulsions. In spinal meningitis both the anterior and posterior roots are affected. The posterior root^^ is the sensory, or afferent, root. It is larger than the anterior root, except in the case of the first cervical nerve; and is composed of from six to eight fas- (47) Radix anterior. (49) Radix posterior. (48) Radix posterior. THE SPINAL CORD. l8l ciculi^ which also combine at once into two bundles. The posterior root pierces the dura mater separately. It unites with the anterior root in the intervertebral foramen. Near the outer end, it presents a swelling which contains large vesicular-bodied nerve cells, and is called a spinal ganglion.^^ (It is occasionally absent on the first nerve.) The posterior root, external to the ganglion, is made up of the dendritic processes (Cajal) of the ganglion cells. These dendrites ex- tend to the most distant parts of the body; they are the sensory fibers of the spinal nerves. Internal to the ganglion, the posterior root is composed of axones, which rise from the ganglion cells. Both the axonic and dendritic processes are medullated. Superficial Origin (apparent central termination). — The posterior roots of the spinal nerves enter the Postero-lateral Fissure ; and, at once, divide into an outer set of small fibers and an inner set of large fibers with some small ones inter- spersed. The fibers of each set bifurcate into a large ascending and a small descending branch. Collaterals rise from the parent axone and from both branches. Deep Origin (real central termination). — The ascending divisions of the outer set of fibers run a short distance along the external surface of the posterior cornu, and end in ramifications about the cell-bodies of the Substantia Gela- tinosa Rolandi. They form the tract of Lissauer. The ascend- ing divisions and collaterals of the inner set of fibers from the posterior root run (1) To the Gray Matter of the Cord, viz. : To all parts of the Posterior Cornu, to the Center of the Crescent, and to the Anterior Cornu on the same side, and, through the gray commissure, to the Center and Cornua of the opposite crescent. Those fibers end in relation with (50) Ganglion spinale. l82 THE BRAIN AND SPINAL CORD. the dendrites or cell-bodies situated in those several regions. (2) To the Brain. Of the ascending fibers from the posterior roots of the spinal nerves, the remainder form the column of Goll and most of Burdach's column and ascend to the Gracile, Cuneate and Rolandic nuclei of the medulla oblon- gata. The greater number terminate in those nuclei, but a few continue, through the external arciform fibers, to the Vermis Cerebelli Superior, and, through the interolivary fil- let, to the Cerebrum. The descending branches of the posterior root-fibers have a short course. They end in the gray matter of the cord. According to Mott some of them enter into the comma tract. They are not well understood. Lesion. — ^The posterior roots of the spinal nerves are first affected (Obersteiner and Redlich) in locomotor ataxia, and the lesion extends to the spinal ganglia (often) and to the posterior columns of the cord. BLOOD SUPPLY OF THE SPINAL CORD. The vessels supplying the cord are the anterior spinal artery^i and the two posterior spinal arteries,^^ which rise at the foramen magnum from the vertebral arteries, and are reinforced by cervical, intercostal and lumbar arteries. The anterior spinal artery descends along the entrance to the anterior median fissure; it is formed by the union of two vessels, one from each vertebral. The posterior spinal artery, of either side, is in reality a pair of vessels which freely communicate, and are so placed as to embrace the posterior nerve roots. The larger vessel of the pair is external to the nerve roots, while the smaller is between them and the pos- (51) Arteria spinalis anterior. (52) Arterise spinales posteriores. THE SPINAL CORD. I83 terior median fissure. The spinal arteries give origin to two sets of branches, namely, the centrifugal and centripetal arteries. Both sets are end-axteries and form rich longitu- dinal plexuses, which overlap each other but do not anas- tamose. The Centrifugal Arteries rise, first and chiefly, from the anterior spinal artery. These enter the anterior median fissure and, running lateralward, supply the greater part of the gray matter. Second, a few centrifugal arteries rise from the posterior spinal arteries. Running into the pos- terior fissure, they are distributed to the posterior white columns, the posterior commissure and to Clark's column of cells. The Centripetal Arteries rise from both the anterior and posterior spinal arteries. They enter the cord at right angles to the surface, and supply the white matter and the peripheral parts of the gray substance, including the tips of the comua. Those branches to the comua accompany the root-fibers. Veins. — The veins^^ ^j^^t carry the blood from the interior of the cord are the fissural veins, which issue from the fissures, the root-veins, which accompany the anterior and posterior root-fibers to the surface of the cord, and a small number of veins that issue from other parts of the surface of the spinal cord. All unite in forming the Medulli-spinal Plexus,^^ spread over the entire surface of the cord beneath the arachnoid membrane. In the upper cervical region, the plexus forms two or three ^mall veins which empty into the vertebral or inferior cerebellar veins ; elsewhere, by a branch along each spinal nerve, the plexus communicates with the (53) Venae. (54) Venae spinales externse. l84 THE BRAIN AND SPINAL CORD. Meningo-rachidian Veins,^^ outside the dura mater, and is drained into the vertebral, intercostal, lumbar and sacral veins. No valves are found in the spinal veins. Lymphatics. — Perivascular and perineural spaces carry the lymph from the spinal cord. There are no lymphatic vessels in the cord. (55) Plexus venosi vertebrales interni. CHAPTER X. TRACING OP IMPULSES. Having studied the grouping and chaining together of neurones, let us now make the knowledge practical by tracing impulses through the better known paths formed by these various neurone groups. The paths thus formed are of three kinds, namely: I. Efferent, or motor; II. Afferent, or sensory — ^General and Special sense; and III. Reflex. I. Efferent, or Motor, Paths. The Pyramidal Paths are direct, as they do not pass through the cerebellum. Their impulses ultimately run either through the spinal or the cranial nerves, and are both motor and inhibitory. Hence the increased reflexes and spastic con- tractions of lateral sclerosis. 1. Through the Spinal Nerves. — Starting in the upper three-fourths of the Rolandic area of the cerebral cortex,, motor and inhibitory impulses run down through the corona radiata, the anterior two-thirds of the posterior segment of the internal capsule, the middle three-fifths of the crusta, the ventral longitudinal fibers of the pons, and the pjrramid of the medulla oblongata, whence they proceed either by the crossed or uncrossed (direct) pyramidal tract to the anterior gray cornu in the opposite side of the spinal cord. By the former route, the impulses cross over in the medulla, through the decussation of the pyramids, and descend in the lateral column of the spinal cord; but by the uncrossed route, they descend in the anterior column of the cord and decussate, l86 THE BRAIN AND SPINAL CORD. in succession, through the white commissure. Impulses by either route finally reach the anterior gray comu of the spinal cord and, with the exception of a small per cent of them, they reach the cornu opposite to their Eolandic origin. The few undecussated fibers in the crossed pyramidal tract conduct uncrossed impulses to the anterior comu of the same side. Thus are explained two symptoms of hemiplegia, viz., weakness on the well side and slight motion on the paralyzed side. From the anterior gray cornu of the spinal cord the nerve commotions are conducted by the efferent, or motor, fibers of the spinal nerves to the muscles of the neck, trunk and extremities. 2. Through the Cranial Nerves. — Impulses destined to the cranial nerves run chiefly from the lower two-fourths of the Rolandic area through corona radiata, genu of internal capsule and on, by the same path as the impulses to spinal nerves, down to the point where they leave the pyramidal tract to enter the nuclei of the cranial nerves, which they do in the vicinity of the several nuclei. They enter the nucleus of the fourth nerve on the same side, but they cross over to the nuclei of the third, fifth, sixth, seventh, ninth, tenth, eleventh and twelfth cranial nerves of the opposite side. By the above nine nerves innervation is conducted to the muscles of the orbit; the muscles of mastication, and expression; the muscles of the tongue, palate and ear; the digastric and styloid muscles; the muscles of the larynx, trachea and bronchi, and of the pharynx, oesophagus, stomach, and the intestines down to the^ rectum. And inhibitory impulses are carried to the heart. The Cerebro-corticopontal Paths, Frontal and Tem- poral. — These paths are indirect, for spinal nerves, since they run through the cerebellum. Frontal. — The impulses TRACING OF IMPULSES. 187 originate in the prefrontal region, at the anterior end of the superior and at the foot of the middle and of the inferior frontal gyri, and descend through corona radiata, the an- terior segment of the internal capsule and the inner (medial) fifth of the crusta; or Temporal. — They rise in the temporal cortex and run through corona radiata, the posterior seg- ment and inferior lamina of the internal capsule, and the outer (lateral) fifth of the crusta. In both paths they run to the nucleus pontis of the same side and to motor nuclei of the cranial nerves, whence they proceed to spinal or cranial nerves. (1) To spinal nerves they run through the middle peduncle of the cerebellum to the cerebellar cortex and, thence, continue down the antero-lateral descending cere- bellar tract to the anterior gray horn of the spinal cord. Their course from the cerebellar cortex is through the resti- form body, the lateralarea of the medulla and the antero- lateral column of the cord. From the gray matter of the spinal cord the impulses are conveyed by the motor fibers of the spinal nerves to the muscles which they supply. (2) To cranial nerves, the impulses run from the synapses formed in the cranial nuclei, by the fibers of the fronto-pontal and temporo-pontal tracts, through the motor fibers of the nerves to their distribution. The Path Through the Intermediate Bundle of the Crusta. — Cortical impulses of unknown origin are received by the corpus striatum and conveyed by a bundle of centrif- ugal axones, which form the deep portion of the crusta, to the nucleus pontis, chiefly of the same side. The impulses thus traverse the internal capsule and a broad but thin area in the crusta just ventral to the substantia nigra and dorsal to the pyramidal tract. From the nuclei pontis, they proceed to the cerebellar cortex by way of the middle peduncle of the 188 THE BRAIN AND SPINAL CORD. cerebellum, and may continue down the descending cerebellar tract as already given. Paths Through the Red Nucleus. — There are two, a direct and an indirect. Impulses run from some part of the cerebral cortex to the optic thalamus and red nucleus or to the corpus striatum and red nucleus. From the red nucleus they pursue either a direct or indirect route. (1) Direct Route. — ^By the direct route, impulses run through the crossed descending tract of the red nucleus to the center of the gray crescent in the opposite side of the spinal cord. Crossing the median raphe at once, in the hypo- thalamic region, the impulses descend by way of the above tract through the ventral part of the formatio reticularis of the mid-brain and pons, in the medial part of the lateral fillet, then through the lateral area of the medulla among the fibers of the antero-lateral ascending cerebellar tract, and finally down the spinal cord, through the dorso-lateral portion of the crossed pyramidal area, to their destination in the gray matter. From the center of the gray crescent they pro- ceed with or without interruption to the anterior roots of the spinal nerves, and are conducted to the muscles. (2) Indirect Route. — Impulses from the red nucleus may also run through the superior cerebellar peduncle, chiefly the opposite one, to the corpus dentatum, and thence, by axones from that nucleus, to the cortex of the cerebellum. The descending cerebellar tract continues their path to the an- terior comu of the cord. Short Fiber Paths. — Those are paths in the formatio reticularis chiefly. (1) Impulses having reached the great ganglia of the cerebrum and mid-brain may run down the formatio reticularis of mid-brain, pons and medulla and the TRACING OF IMPULSES. I89 antero-lateral ground bundle of the spinal cord to the gray crescent of the same, and continue through the anterior root fibers to their destination. On the other hand, the impulsefi, leaving formatio reticularis in mid-brain, pons or medulla, may enter the nuclei of motor cranial nerves and be con- ducted by them to tlie muscles supplied by cranial nerves. (2) The impulses may leave the formatio reticularis in the pons, and run to the cerebellar cortex through the middle peduncle of the cerebellum. From the cerebellum they may follow the ordinary course through the descending cerebellar tract to the anterior gray horn of the cord; or (3) Impulses having arrived at the cerebellar cortex by way of the superior or middle peduncles, may descend through the cerebello- olivary tract, in the restiform body, to the opposite inferior olive, and be carried on through descending axones of the olive, in the antero-lateral ground bundle, to the gray matter of the cord (Koelliker). (4) Impulses descend from the nucleus of the third cranial nerve by way of certain fibers in the posterior longitudinal bundle to the seventh nerve, where it enters into the eminentia teres, and through the facial nerve innervate the frontalis, pyramidalis nasi, corrugator supercilii and orbicularis palpebrarum. Hence these muscles are not paralyzed in nuclear facial paralysis. But if the lesion be in the eminentia teres or distal to it, then facial paralysis is complete. (5) Through certain fibers in the posterior longitudinal bundle which rise in the nucleus of the sixth cranial nerve and cross to the opposite nucleus of the motor oculi, impulses run from the nucleus of the abducent through the opposite third nerve to the internal rectus oculi. They explain the conjugate deviation observed in lesions affecting the nucleus of the sixth nerve. In nudear lesions of the abducent nerve the external rectus of the same eye 190 THE BRAIN AND SPINAL CORD. and the internal rectus of the other eye are paralyzed if the nucleus is destroyed and stimulated if the nucleus is only irritated. II. Afferent, or Sensory, Paths. The sensory paths conduct two varieties of impulses, viz., General and Special.. The impulses originate in the end- organs of the cranial and spinal nerves, and by those nerves are conveyed to the cerebro-spinal axis, through which they reach the proper cortical area in the cerebrum. 1. General Sensation. Through Columns of Goll and Burdach. — GolFs col- umn is believed to carry impul'ses of the muscular sense, while impulses of all varieties of general sensation are transmitted by Burdach^s column. Impulses originating in the end organs of the spinal nerves traverse the dendrites of the spinal ganglion neurones, the cell-bodies in the ganglia (Cajal), and then the axones of the same. They enter the cord through the posterior roots of the spinal nerves, and ascend through the tracts of Burdach and Goll, in the posterior column of the cord, to the nuclei of that column in the medulla oblon- gata, chiefly the nucleus gracilis and nucleils cuneatus. Thence the impulses may proceed either by a direct or by an indirect route. (1) The Direct Route carries the impulses by way of the interolivary and medial fillet, through the sensory decussation of the medulla, the formatio reticularis of pons and mid-brain and the crusta of the mid-brain, to the ventro-lateral nucleus of the optic thalamus, from which they are conducted by the three systems of Flechsig — namely, the anterior stalk of the thalamus, the ansa peduncularis and the ansa lenticularis — to the somsesthetic area of the cerebral cortex. In their last TRACING OF IMPULSES. IQI stage the impulses run from the optic thalamus through the internal capsule and corona radiata to the equatorial zone of the hemisphere. (2) Indirect Route. — By that route impulses from the nucleus gracilis and nucleus cuneatus run to the cortex of the vermis cerebelli superior through the external arciform fibers; then on^ through the superior peduncle of the cere- bellum, to the red nucleus and optic thalamus. They traverse the restiform body of the same side, by way of the posterior external arciform fibers; or, by way of the anterior external arciform fibers, they traverse the sensory decussa- tion of the medulla and the opposite restiform body to reach the vermis cerebelli superior. From the cerebellar cortex, the impulses continue through cortical axones to the corpus dentatum, whose axones conduct them to the red nucleus and optic thalamus of the opposite side. The greater number, therefore, cross over in the tegmentum of the mid-brain. Their course from the red nucleus and optic thalamus is through the three systems of Flechsig to the cortex. Through Cranial Nerves and Medial Fillet. — As crossed fibers from the terminal nuclei of the trifacial, the vestibular, the glossopharyngeal and the pneumogastric nerves join the medial fillet and run to the optic thalamus, so impulses of common sensation, transmitted by those cra- nial nerves to the medulla and pons, are carried by the medial fillet to the ventro-lateral nucleus of the thalamus on the opposite side. The systems of Flechsig, chiefly the ansa peduncularis, conduct them to the lower portion of the somaesthetic area. Through Direct Cerebellar Tract. — Clark's column of cell-bodies in the spinal cord receives impulses concerning equilibrium from the posterior roots of the spinal nerves and 192 THE BRAIN AND SPINAL CORD. transmits them at once to the direct cerebellar tract through which they ascend along the dorso-lateral surface of the cord, along the posterior surface and through the restiform body of the medulla to the cortex of the superior worm of the cerebellum. To a small extent they cross in the worm to the opposite side. From the cerebellar cortex the journey is completed in four stages, as already described, namely: Corpus dentatum, opposite red nucleus, optic thalamus and cerebral cortex. Through Antero-lateral Ascending Cerebellar Tract. — Pathetic and thermic impulses are conveyed by this tract. Those impulses enter the center of the gray crescent of the cord, partly on the same side, through the posterior nerve roots and Burdach's column. A large number decus- sate in the above cerebellar tract, crossing in the anterior commissure, and run upward through the antero-lateral ascending cerebellar tract of the opposite side to the cortex of the superior worm of the cerebellum and to the optic thalamus. In the cord they ascend along the ventro-lateral surface. They run dorsal to the olive in the lateral area of the medulla oblongata, and through the lateral part of the formatio reticularis of the pons to the angle in Gower's tract. Prom the angle, just behind the quadrigeminal bodies, the greater number of impulses run backward with the tract through the valve of Vieussens to the cortex of the vermis cerebelli superior; the remainder run forward to the optic thalamus, and from that to the parietal cortex. The common course of sensory impulses from the cerebellar to the cerebral cortex is, as already described, through corpus dentatum and superior peduncle to opposite red nucleus and optic thalamus, though they may run through the middle cere- bellar peduncle to the pons and then, by way of the formatio TRACING OF IMPULSES I93 reticularis, the medial fillet, or the posterior longitudinal bundle, ascend to the optic thalamus. Having arrived in the thalamus, they proceed thence by the three systems of Flech- sig to the soma^sthetic cortex. The Short Fiber Paths. — (1) The antero-lateral ground bundle and formatio reticularis contain ascending axones which may convey sensory impulses from the gray matter of the cord, received from the posterior roots of the spinal nerves, or from terminal nuclei in medulla and pons which receive the common sensory fibers of cranial nerves, upward to the optic thalamus of the opposite side. The course from the thalamus by way of the cortical fillet is now familiar. (2) Again, impulses may leave the formatio reticularis in the pons and run through the middle cerebellar peduncle, by way of axones from the nuclei pontis, to the cortex of the cerebellum ; and then continue by the ordinary course through the superior peduncle to the red nucleus and optic thalamus. (3) Certain fibers of the antero-lateral ascending cere- bellar tract diverge from the others, in the medulla oblongata, and terminate in the lateral nucleus. Impulses of pain and temperature, following the same course, enter the lateral nucleus, and are carried on through the restiform body to the cerebellum by the tract from the lateral nucleus to the cerebellar cortex, thence to the somsesthetic area as previously given. Destruction of any of the above sensory paths causes loss of the especial variety of impulse which travels that path. Destruction of G oil's column produces loss of muscular sen- sations, and cases are on record in which a cord lesion abolished pain and temperature seusations while touch was not affected. 194 the brain and spinal cord. 2. Special Sensations. Impulses producing the sensations of smell, sight, hearing and taste are carried from the respective organs of sense to the brain by the following nerves: The Olfactory; the Optic; the Auditory; and the Glossopharyngeal, chorda tympani and pars intermedia. Olfactory Path. — Impulses of smell originate in the upper third of the Schneiderian membrane. They run through the olfactory nerves to the second layer in the bulb, where they are transferred to the dendrites of the mitral cells. By the axones of the mitral cells they are carried backward through the olfactory tract and roots to the cere- bral hemisphere. The internal, or medial, root conducts them to the area of Broca and anterior end of the gyrus f orni- catus, whence through the cingulum and uncinate fasciculus they reach the cortical area of smell in the uncus hippocampi. By the middle olfactory root the impulses enter the trigone and complete their journey either in the same manner as given above or via the anterior commissure. The external, or lateral, root of the olfactory tract conducts the impulses directly to the uncus of the hippocampal convolution. Note that olfactory impulses are chiefly, if not entirely, uncrossed. Optic Path. — ^Impulses of sight originate in the rods and cones of the retinae and traverse three or more series of neurones to the terminal nuclei of the optic tracts; namely, the rod and cone, the bipolar and the ganglionar neurones. The axones of the last form the optic nerves arid the visual part o-f the optic tracts. From the right halves of both retinae and from the left halves of both, impulses run through the corresponding tract to the external geniculate body and the pulvinar of the optic thalamus; also to the superior quadrigeminal body and the nudeus of the motor oculi nerve. TRACING OF IMPULSES. I95 The two latter produce ocular and pupillary reflexes. From the lateral geniculate body and pulvinar the optic radiations carry the impulses through the posterior segment of the in- ternal capsule to the half-visual center in the cuneus and (to a small extent) the convex part of the occipital lobe. Impulses from the nasal halves of the retinae decussate in the optic commissure; those from the temporal halves, for the most part at least, remain on the same side, but a few may cross through the quadrigeminal bodies and superior brachia. Auditory Paths. — There are two auditory paths, the Cochlear and the Vestibular. The former is concerned with hearing and the latter with equilibrium. 1. The Cochlear Path. — Impulses of hearing originate in the organ of Corti. They are transmitted by the rods and hair cells of Corti to the dendrites of the spiral ganglion. Traversing the dendrites and cell-bodies of that ganglion, they enter the axones, which form the cochlear nerve, and run backward to the terminal nucleus of that nerve in the me- dulla. Both the ventral and the dorsal, or lateral, portions of the cochlear nucleus (ventral auditory nucleus) receive the impulses of hearing. From the cochlear nucleus they run either lateral and dorsal to the restiform body and cross to the opposite side through the acustic striae and trapezium, or they run medial to the restiform body and enter at once into the trapezium. By either course they reach the lateral fillet, and chiefly the opposite one. The lateral fillets con- duct the impulses to the inferior quadrigeminal bodies; the inferior brachia to the internal geniculate bodies, and the acustic radiations to the third and fourth fifths of the supe- rior temporal and to the transverse temporal gyri of the cerebrum. 2. Vestibular Path. — The extent of the vestibular conduc- 196 THE BRAIN AND SPINAL CORD. tion path is from the acustic areas of the utricle saccule and semi-circular canals to the vestibular nuclei in the floor of the fourth ventricle and, thence, to the cerebellum and the corti- cal area of equilibrium in the parietal cortex. It is the path of the space sense. Through the vestibular nerve the im- pulses reach the dorso-medial, dorso-lateral and superior auditory (vestibular) nuclei in the floor of the fourth ven- tricle and the spinal nucleus, which has not been definitely located, and they probably reach the nuclei in the cerebellum also (globosus and fastigii). The impulses may pursue, from the terminal nuclei in the ventricular floor, either a direct or an indirect course to the cerebral cortex. (1) By the direct course they run through the opposite medial fillet and certain fibers in the three systems of Flech- sig(?). (2) The impulses run to the cerebellum, by the indirect course, through the acustico-cerebellar tract, and probably through uninterrupted fibers of the vestibular nerve in the restiform body. They thus reach the opposite nucleus fastigii and nucleus globosus; perhaps a number also reach the corpus dentatum and cerebellar cortex. From the cere- bellum the course of the impulses is, presumably, through the superior peduncle to the red nucleus and optic thalamus of both sides and thence to the cortex. They may excite in the cerebellum impulses of equilibration which descend to the motor nuclei of spinal nerves in the anterior horns of gray matter by way of the antero-lateral descending cerebellar tracts. Impulses, believed to be concerned with reflexes, run from the vestibular nuclei in the floor of the fourth ventricle (a) to opposite nuclei of motor cranial nerves via the posterior longitudinal bundle; (b) to the quadrigeminal bodies through TRACING OF IMPULSES. 197 the superior and lateral fillets; and (c) to the inferior olive and lateral column of the spinal cord by way of the vestibnlo- olivary and vestibulo-spinal fibers. The Gustatory Paths. — They extend from the tongue to the glossopharyngeal nucleus in the medulla and thence through the opposite medial fillet and inferior lamina of the internal capsule to the taste area in the gyrus hippocampi. There are two paths from the tongue to the ninth nucleus. Those impulses from the base of the tongue and the palate run through the ninth nerve and those from the anterior two-thirds of the tongue through the chorda tympani and pars intermedia to the medulla (A. F. Dixon) (see note). Pos- sibly, gustatory impulses originating in the palate may traverse the descending branches of Meckel's ganglion and the great superficial petrosal nerve to reach the geniculate ganglion on the facial ; and, then, continue through the pars intermedia to the glossopharyngeal nucleus. All impulses arriving at this nucleus complete their journey in two stages: First, through the medial fillet to the opposite thalamus; and, second, through internal capsule to the hippocampal cortex. Destruction of the olfactory conduction path on one side causes anosmia on the same side ; of the optic tract or radia- tions, hemianopia in the corresponding halves of both retinae ; of the auditory path above the pons, deafness chiefly on the opposite side; and interruption of the gustatory path above the medulla oblongata abolishes taste on the opposite (?) side. Note.— Edinbg. M. J., 1897, Vol. I, p. 395, A. F. Dixon. Amer. J. Med. Science, 1898, Vol. I, pp. 502-532, Cases VI and VII, Keen and Spiller. 198 THE BRAIN AND SPINAL CORD. III. Keflex Paths. There is no visible limit to the number of reflex paths. Hence no attempt will be made to give them completely, but a few examples of various kinds will be given which may assist the student to trace others and be suggestive of their great multiplicity and importance. Eeflex arcs are formed ( 1 ) by the sensory and motor fibers of spinal nerves, associated in the gray matter of the cord; (2) by the sensory and motor fibers of cranial nerves, which are connected in the brain; (3) by afferent spinal fibers, the posterior longitudinal bundle, chiefly, and efferent cranial fibers; and (4) by afferent cranial and efferent spinal nerve fibers, the two being associated by the anterior longitudinal bundle, the spinal root of the fifth nerve, the vestibulo- olivary and vestibulo-spinal tracts, the solitary bundle, etc. (1) Spinal Reflexes. — In the simplest spinal reflexes^ the afferent fibers of the arc arborize about the cell-bodies whose axones constitute the efferent fibers. Among them are the skin and muscle reflexes, such as the plantar, the patellar, the gluteal and the cremaster reflexes, the involuntary with- drawing of a part from a source of irritation, etc. More complicated spinal reflexes are those of defecation, micturition, parturition, vasomotor reflexes, cardio-accelera- tor reflexes, etc. The impulses traverse at least three neurones in these reflexes. As an example, trace a defecation reflex. Defecation Befiex. — ^The rectum is supplied by the third and fourth sacral nerves and by branches of the inferior mesenteric and hypogastric plexuses. Irritation of the sen- sory endings in the mucous membrane is caused, normally, by the presence of feces. The impulses caused thereby run to the special defecation center in the lumbar enlargement of the spinal cord, either by way of the sacral nerves or through TRACING OF IMPULSES. 199 the sympathetic plexuses, the ganglionated cord, and the rami communicantes to the lumbar nerves, through the pos- terior roots of which they reach the center in the cord. From the defecation center the impulses pursue two courses: (a) They descend through the third and fourth sacral nerves and cause inhibition in the circular fibers of the rectum and contraction of the longitudinal muscle, (b) This action is immediately followed by impulses which pursue the sympa- thetic course, through the anterior roots of the lumbar nerves, the rami communicantcs, the ganglionated cord, and the in- ferior mesenteric and hypogastric plexuses, to the rectum. They cause, in succession from above downward, contraction of the circular muscle of the rectum. The two series of impulses thus open a way for the passage of fecal matter; and, then, force it through the opening unless prevented by the voluntary contraction of the external sphincter. (2) Cranial Reflexes. — The simplest of these reflexes are such as spasm of the muscles of mastication caused by a bad tooth, in which both limbs of the arc are formed by the trifacial nerve. Again, the facial expression of pain due to the same cause. In this the impulses traverse the trifacial nerve and by the collaterals of its root-fibers reach the nucleus of the facial. Through the facial they cause contraction of certain muscles of expression. Salivary reflexes, in which the sight of a fine dinner or the smell of it causes the flow of saliva; coughing, sneezing, vomiting reflexes and deglutition reflexes are more compli- cated, but, knowing the nerve supply of the parts involved, the student can trace the impulses. (3) Spinal and Cranial Reflexes. — Impulses received by the spinal cord through the afferent fibers of its nerves are transmitted by the posterior longitudinal bundle to the 200 THE BRAIN AND SPINAL CORD. nuclei of motor cranial nerves, or, perhaps, through Burdach's column and the interolivary fillet to the same nuclei. Thus is brought about the movement of the eyes toward the source of impulse, a change of facial expression to agree with the painful or pleasing character of the impulses, etc. (4) Cranial and Spinal Reflexes. — Of these there are many. Let us notice three. Respiratory Reflex. — Any obstruction or irritation in the larynx or trachea sends an impulse through the pneumo- gastric nerve to its sensory nucleus and, through its descend- ing branches, in the solitary bundle, to the nucleus ambiguus and nucleus of the phrenic nerve in the cervical cord, causing increased respiratory effort, coughing, spasm of muscles closing the glottis, etc. Auditory Reflex. — Turning of the head upon hearing a sound, and the sudden starting, caused by hearing a loud sound, are illustrations of this reflex. The path for the latter is probably as follows: The auditory nerve, the vesti- bulo-olivary and vestibulo^spinal tracts, antero-lateral ground bundle and efferent fibers of spinal nerves. Pupillary Reflexes. — Pupillary reflexes belong to the cra- nial and cranio-spinal group of reflexes. The cilio-spinal centers are in the cervical enlargement of the spinal cord, the pupillo-dilator in the upper and the pupillo-constrictor in the middle part of that enlargement. They receive optic im- pulses through the anterior (or ventral) longitudinal bundle from the corpora quadrigemina superiora. The superior quadrigeminal bodies receive those impulses by two routes: First, directly, through the fibers of the external root of the optic tract, and, second, indirectly, through centrifugal fibers in the optic radiations, and the superior brachium. By the latter route, the optic impulses which have xeached the visual TRACING OF IMPULSES. 201 area of the occipital lobe, by way of the intrinsic retinal neurones and the optic nerves, tracts and radiations, are returned to the optic thalamus and external geniculate body and then carried back to the superior quadrigeminal bodies. Thence, reaching the cilio-spinal centers through the anterior longitudinal bundle, the impulses take one of two courses: (a) They leave the spinal cord through the anterior roots of the upper thoracic nerves and run, in succession, through the rami communicantes, the cervical cord of the sympathetic, the cavernous plexus^ the ciliary ganglion and the short ciliary nerves to the radiating fibers of the iris, causing dila- tion of the pupil, (b) From the pupillo-constrictor center, the impulses are carried upward by the posterior longitudinal bundle to the nuclei of the motor oculi nerve, where they are reinforced by optic impulses received directly through the superior quadrigeminal body and posterior commissure. The impulses reach the ciliary muscle and the circular muscle of the iris through the motor oculi, ciliary ganglion and short ciliary nerves. The results are contraction of the pupil and accommodation for distance. CHAPTER XI. EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. The brain and spinal cord are developed from the neural tube; the spinal and sympathetic ganglia and the ganglia of sensory cranial nerves are derivatives of the neural crest. Very soon after conception there appears along the median line, in the back of the embryo, a plate of epiblast, called the medullary plate. That plate soon presents two longitudinal elevations, the medullary ridges, separated by a median fur- row, the neural groove. The rapid growth and infolding of the medullary ridges roofs over and closes in the neural groove and thus forms the neural tube. That approxima- tion of the medullary ridges produces a slight median eleva- tion, which is the neural crest. By the fifteenth day after conception the neural tube and crest are complete, except posteriorly, where the neural groove is stiU open. Meninges. — Later the neural tube becomes surrounded by mesoblast which forms the pia mater, arachnoid and dura mater. The Neural Crest. — (1) The cephalic portion of the neural crest becomes broken into five pairs of ganglia, which, during development, shift their positions to the ventral side of the brain. Those ganglia are called the Jugular, Petrosal, Genic- ulate, Auditory and Gasserian. They give origin to the sensory parts of the pneumogastric, glossopharyngeal and facial nerves; all of the auditory nerve, and the sensory part of the trifacial. In all of the ganglia, except the auditory, EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 2O3 the cells develop into unipolar neurones ; they remain bipolar in the auditory ganglion. The single processes of the uni- polar neurones immediately divide, T-like, into peripheral and central fibers, which in appearance are axones. The peripheral fibers form the sensory part of the respective nerves and conduct impulses toward the cell-body, hence they may be considered dendrites (Cajal) ; the central fibers, the axones proper, form the part of the sensory nerve between the ganglion and the brain. From the auditory ganglion, which moves backward to a point behind the geniculate ganglion, the dendrites run outward to the acustic areas of the internal ear; the axones enter the medulla oblongata. All the central axones of the several ganglia divide, T-like, upon entering the brain, and collaterals rise from the un- divided fibers and from both branches of them. These axones and collaterals arborize, chiefly, in the terminal nuclei of the respective nerves; but certain of them, the excito- reflex fibers, terminate in nuclei of motor nerves. (2) The spinal portion of the neural crest forms the thirty-one pairs of Spinal Ganglia situated on the posterior nerve-roots ; and, also, the Vertebral, Prevertebral and Termi- nal Ganglia of the sympathetic system. The sympathetic ganglia wander widely. In them the epiblastic cells develop into multipolar neurones, the nonmedullated processes of which constitute the larger number of gray fibers in the sympathetic system. The cells of the spinal ganglia form unipolar neurones, like those of the jugular, petrosal, genicu- late and Gasserian ganglia. Like them, also, the single processes divide, T-like, the peripheral arms of the T- branches forming the sensory part of each spinal nerve and the central arms (the axones) the posterior roots of those nerves. The latter enter the cord at the postero-lateral fis- 204 THE BRAIN AND SPINAL CORD. sure and, before and after dividing T-like into an ascending and a descending branch, give off collaterals. The descending fibers (axones and collaterals) arborize in the gray matter of the cord; the ascending axones and collaterals terminate chiefly in the spinal cord, and in the nuclei of its posterior columns, namely, the nucleus gracilis and nucleus cuneatus. A few ascending fibers end in the cerebellum and cerebrum. The Neural Tube.— It is well formed at the fifteenth day. The cephalic, or closed, end of the tube is much larger than the caudal end, and presents at this time two constrictions that separate the Primary Brain Vesicles from one another — the anterior, the middle and the posterior. Behind the poste- rior primary vesicle, the neural tube remains small and of nearly uniform size ; that part forms the spinal cord. The neural tube, up to the fourth week, is composed of a single layer of long columnar cells whose ends form the exte- rior and interior surfaces of the tube. The cells contain a nucleus in their middle third and present a central and a peripheral clear zone. In the central clear zone, near the interior surface of the tube, there may be observed between the fourth and the fifth week a number of small, round, nucleated cells, the nuclei of which are in all stages of karyokinesis. These are the germinating cells (His) . Soon they become elongated and send out a protoplasmic process from what was originally (i. e., before the formation of the neural tube) the deep, or proximal, end of the cell. Now they are neuroblasts, because they are the parents of the neurones. The protoplasmic processes form the axones, and other processes may or may not develop. Both the axones and dendrites grow in the direction of least resistance (His). While the neuroblasts are developing, the columnar cells of the neural tube undergo great changes. They become more EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 205 and more elongated and, by a process of vacuolation, their protoplasm becomes perforated and branched and so broken up a;S to entirely destroy the original outlines of the cells. The branches appear to unite and form a sort of radial net-work in the peripheral clear zone, called the myelospon- yium. The elements of the myelospongium are the spongio- blasts; they form the neuroglia. At this time the Three Histologic Layers begin to show, namely, (1) the outer layer (neuroglia), (2) the middle, or mantle, layer, composed of neuroblasts, and (3) the inner, or ependymal, layer; also at this time a lateral longitudinal groove appears, which extends from the mesencephalon to the caudal end of the tube. The groove is on the ventricular surface. It gives the lumen of the tube a diamond shape, on section, and separates the ventral from the dorsal zone. The ventral zone is motor and the dorsal is sensory. BRAIN. The brain vesicles grow rapidly. By the end of the fourth week a constriction is visible in the anterior primary vesicle and another in the posterior primary vesicle, dividing each into two and making in all Five Secondary Brain Vesicles, which freely communicate with one another and are numbered from before backward. They are: 1. Prosencephalon, or telencephalon. 2. Thalamencephalon, or diencephalon. 3. Mesencephalon. 4. Epencephalon. . 5. Metencephalon, or myelencephalon. These vesicles form the brain, their cavities becoming the ventricles. The neuroblasts of the mantle layer produce the neurones, whose cell-bodies and dendrites are found in the cortex and ganglia, and whose medullated axones form 206 THE BRAIN AND SPINAL CORD. the white substance. The supporting neuroglia is formed by the spongioblasts of the neurogliar and ependymal layers. Flexures. — The cephalic portion of the neural tube is the seat of three flexures, two ventral and one dorsal. (1) The mesencephalic flexure (ventral) begins very early and amounts to nearly 180 degrees by the twenty-eighth day. It bends ventrally the thalamencephalon until it almost touches the epencephalon. Thus the inter-brain and pons are ap- proximated. (2) The cervical flexure is also a ventral one, It is located at the junction of the fifth vesicle with the spinal cord, and corresponds to the bending of the head upon the body of the embryo. This flexion begins about the twenty- first day. By the end of the fourth week, it is completed and amounts to 90 degrees. (3) The dorsal flexure is be- ginning to form at the same time (fourth week). It occurs between the fourth and fifth brain vesicles, and is often called the metencephalic flexure. It reaches 180 degrees by the eighth week, when the dorsal part of the epencephalon (the cerebellum) rests upon the metencephalon (the medulla oblongata). The cervical and metencephalic flexures almost entirely disappear, but the mesencephalic flexure is perma- nent. . EMBRYOLOGY OF THE BRAIN AND SPINAL CORD. 207 TABLE III. BEAIN VESICLES AND THEIB DEBIVATIVES. Primary Vesicles. Secondary Vesicles. ' 1st. The Prosenceph- *j alon. Anterior (Fore-brain) 2d. The Thalamen- cephalon. Middle (Mid-brain). 3d. The Mesencepha- lon. Derivatives and Ventricles. Hemispheres and An- terior wall of third ventricle. (Foram- ina of Monro, lateral ventricles, hemispheres, cor- pora striata, olfac tory lobes, fornix, anterior commis- sure, corpus cal- losum and lamina terminalis.) Inter-brain and third ventricle, ex- cept anterior wall. (Optic thalami, ex- ternal geniculate bodies, posterior and middle com- missures, pineal body, roof epithe- lium of third ven- tricle and the third ventricle, corpora albicantia, tuber cinereum and in- fundibulum, lami- na cinerea, retinae, optic nerves, chiasm and tracts.) Mid-brain and Aqe- duct of Sylvius. (Crustae, substan- tia nigra, tegmen- tum. Sylvian aque- duct, corpora qua*- rigemina and in- ternal geniculate bodies.) 208 THE BRAIN AND SPINAL CORD. Posterior (Hind-brain). J 4th. TheEpencepha. rHi"4~^ JJ^^ e g ""'■ I lum.) •